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INVESTIGATIONAL · PHASE 2 RESULTS · NOT FDA-APPROVED

By The RX Index Editorial TeamLast updated: Last verified: Version 1.0Next scheduled review: September 2026

Bimagrumab Weight Loss Drug: 2026 Results, Side Effects, and Whether You Can Get It

A source-normalized review of the BELIEVE trial and the earlier 2021 study: what the 22.1% and 10.8% results do and don't support, what is in development, and why there is no bimagrumab you can get today.

Affiliate disclosure: The RX Index may earn a commission if you choose certain providers through our links. That never changes the trial data, the FDA status, or the conclusions on this page. Bimagrumab itself is investigational—we are not recommending it, and there is no approved bimagrumab product for sale to patients.


The 22.1% headline, translated

The bimagrumab weight loss drug is investigational—not a GLP-1, not FDA-approved, and not available as a routine prescription. In its biggest published trial, bimagrumab alone was linked to 10.8% average weight loss at 72 weeks—and 22.1% when combined with semaglutide. What made researchers sit up wasn't only the weight. It was the body composition: people on semaglutide alone lost 7.4% of their DXA-measured lean mass. People on high-dose bimagrumab alone gained 2.5%.1

That's the headline. Here's the part almost nobody reports.

Those 72-week numbers came from analyses the study authors labeled post hoc, and no adjustment was made for multiple comparisons. The authors wrote plainly that the results should not be used to draw definitive treatment conclusions. In the bimagrumab-only groups, 14.0% to 21.4% of participants stopped treatment because of adverse events. And as of August 4, 2026, no Phase 3 bimagrumab obesity trial was publicly listed in ClinicalTrials.gov or Lilly's public trial program.12

We also compared BELIEVE's two prespecified week-48 estimands. The incremental difference between the high-dose combination and semaglutide 2.4 mg was 2.9 percentage points under the treatment-regimen estimand and 5.4 points under the efficacy estimand—nearly twice as large depending on the analysis question. That does not decide approval. It shows why the biggest headline cannot stand alone.1

We'll show you that math, with the limits attached.

What changes the answer for you: if you're already on a GLP-1 and worried about muscle, this drug is not a current option and there are things you can discuss with your clinician now. If you're thinking about delaying treatment until bimagrumab arrives, there is no verified launch year to plan around. And if someone is offering to sell it to you, skip to the arithmetic in “Can you buy bimagrumab online?”—a representative 5 mg research-use vial is about 0.16% of the high trial amount calculated for BELIEVE's average participant.

Quick answers

Quick answers
QuestionAnswer
Is bimagrumab FDA-approved?No. No FDA-approved bimagrumab product exists
Can a doctor prescribe it routinely?No. Trial participation is the identifiable access path; exceptional investigational-access pathways are not routine prescriptions
Is it a GLP-1?No. It is a different drug class
What is it?An investigational monoclonal antibody that blocks activin type II receptors
Best published result on its own10.8% modeled average weight loss at week 72
Best published combination result22.1% with high-dose bimagrumab plus semaglutide at week 72
Did it stop all lean-mass loss?No. The high-dose combination group still lost 2.9% of DXA-measured lean mass
How was it given?BELIEVE used a 30-minute IV infusion at a clinical site, with loading doses and then dosing every 12 weeks
Development stagePhase 2 obesity development; no public Phase 3 obesity registration found at verification2
PriceNo verified commercial price exists
Last verifiedAugust 4, 2026

Best for you if: you saw a bimagrumab headline and want to know what it actually means, or you're on a GLP-1 and worried about losing lean mass.

Not for you if: you're looking for a prescription, a price, or a launch date. None of those exists as a verified commercial fact.

The RX Index is the independent GLP-1 decision resource that scores telehealth providers and treatment paths on clinical legitimacy, care quality, transparency, access, and cost, so readers can choose the path that fits their situation.

The right GLP-1 provider isn't the same for everyone—it depends on your state, your insurance and formulary, whether you want an FDA-approved or compounded medication, your preferred treatment path (injection or oral), and your budget. Because a general answer can't resolve those for you, use The RX Index's Find My GLP-1 Path tool to get a personalized provider match with source-verified pricing before you choose.

What we actually verified

We didn't summarize the news coverage. We read the sources.

  • The full BELIEVE trial publication in Nature Medicine (March 2, 2026), including the methods, safety tables, statistical plan, and authors' stated limits
  • The earlier 2021 bimagrumab trial published in JAMA Network Open
  • The public records for the completed BELIEVE study, the continuing bimagrumab–tirzepatide program, the Mass General body-composition study, the completed formulation study, and the diabetes study that was withdrawn before enrollment
  • The FDA's public records showing no approval and its rules for compounded biological products
  • The FDA's expanded-access requirements, so the page does not falsely claim that a clinical trial is the only legally conceivable investigational-access pathway
  • BELIEVE's two prespecified week-48 estimands, compared on the same randomized high-dose arms rather than collapsed into one headline
  • BELIEVE's funding and conflict-of-interest disclosures
  • The arithmetic comparing BELIEVE's published estimands and the scale of a representative research-use vial with the amount used in the trial

We did not take a consequential medical or regulatory number from a secondary source when the original was available.


What is bimagrumab, and is it a GLP-1?

Bimagrumab is an investigational monoclonal antibody—a lab-made protein designed to attach to specific biological targets. Its targets are the activin type II receptors ActRIIA and ActRIIB. It is not a GLP-1 receptor agonist. Instead of primarily reducing appetite and food intake, it blocks signaling involved in adipose tissue and skeletal-muscle biology.1

That difference matters more than it sounds.

Semaglutide and tirzepatide work through incretin pathways that affect appetite, food intake, glucose regulation, and other metabolic processes. Bimagrumab does not appear to materially reduce food intake. In BELIEVE at week 24, the median change in daily calories was −182 with high-dose bimagrumab, −482.5 with semaglutide 2.4 mg, −487 with the high-dose combination, and −238.5 with placebo. Same trial, same counseling, very different intake pattern.1

How it works

Your body has a braking system for muscle growth. Proteins including myostatin and activins bind to activin type II receptors and help regulate muscle and fat biology. Bimagrumab blocks those receptors, interrupting several signals at once. Human trials have measured increases in lean mass with bimagrumab, but an increase in DXA-measured lean mass is not automatically the same as more functional skeletal muscle.13

The fat side became more interesting as human genetics clarified the pathway. Large sequencing studies found that rare loss-of-function variants in INHBE, the gene encoding activin E, were associated with more favorable abdominal-fat distribution and lower risk of type 2 diabetes. Those findings helped support the biological rationale for targeting this receptor pathway. BELIEVE then separately showed large reductions in fat mass and estimated visceral adipose tissue in people treated with bimagrumab.451

So a drug first developed for muscle-related disorders became an obesity-development asset. Versanis Bio in-licensed bimagrumab from Novartis and raised a $70 million Series A to advance it in obesity. Eli Lilly later acquired Versanis for up to $1.925 billion.67

One precision point: bimagrumab gets called a “myostatin inhibitor” constantly. That's shorthand, and it's not quite right. It blocks activin type II receptors, which sit downstream of myostatin, activins, GDF11, and related ligands. That makes it a broader pathway intervention than a drug that neutralizes myostatin alone. The breadth does not by itself prove better efficacy or worse safety.

How it was actually given in BELIEVE

This is the detail that most coverage skips, and it changes how you should think about the whole drug.

In BELIEVE, bimagrumab was a 30-minute IV infusion at a clinical site, dosed by body weight. Loading infusions were given at weeks 1 and 4, followed by infusions at weeks 16, 28, 40, 52, and 64. Not a pen in your fridge. Not a weekly shot at your kitchen table. A site-administered infusion schedule with two early loading doses and quarterly maintenance dosing.1

The trial authors flagged the administration method as a possible contributor to early laboratory abnormalities and adverse events. They wrote that subcutaneous dosing may attenuate those effects, based on a formulation-comparison study, and the current bimagrumab–tirzepatide Phase 2 program is evaluating subcutaneous dosing. That possibility is being tested; it is not an established commercial advantage.18

Where it came from

Short version, because it explains a lot of confusing headlines.

Novartis and MorphoSys developed bimagrumab as BYM338 for muscle-related diseases. It failed its primary efficacy endpoint in a large study of sporadic inclusion body myositis.9 Novartis later licensed it to Versanis Bio. Versanis raised $70 million in Series A financing after that in-licensing; the $70 million was financing, not the license price. Two years later, Eli Lilly bought Versanis in a deal worth up to $1.925 billion.67

One correction worth making, because several pages covering this area mix up the companies: bimagrumab belongs to Eli Lilly through its acquisition of Versanis. It is not a Scholar Rock drug. Scholar Rock's muscle-directed drug is apitegromab, a different molecule with a different target.


Is the bimagrumab weight loss drug FDA-approved or available now?

No. As of August 4, 2026, bimagrumab is not FDA-approved for weight loss or any other use. There is no approved dose, pharmacy product, retail price, or routine prescription path. Clinical-trial participation is the identifiable public access route for eligible participants. In the United States, expanded access can sometimes be requested for a serious or immediately life-threatening condition, but it requires a willing physician, manufacturer cooperation, IRB review, and FDA authorization; no public bimagrumab expanded-access program was identified for obesity.1011

Let's be blunt about the most important fact on this page, because it's also the least exciting one.

Bimagrumab is not a treatment you can choose today. The evidence is interesting enough to follow closely. It is nowhere near mature enough to plan your health around, and there is no defensible public basis for promising a launch year.

We'd rather you hear that from us in the first two minutes than find it out after twenty minutes of hope.

What “investigational” actually means here

It does not mean “almost approved.” It means the drug is still being studied and has not been approved for sale.

The public obesity program remains in Phase 2. At verification, we found no Phase 3 bimagrumab obesity study in ClinicalTrials.gov or Lilly's public trial listing.2 A future sponsor could register one at any time, which is why this claim belongs on the monthly refresh list rather than in permanent copy.

So when you see a completion date on a bimagrumab trial, that's the end of that study's listed trial window. Not a launch date. Not an approval date.

Can you join a bimagrumab trial?

Sometimes. It depends on which study is recruiting, where you live, and whether you meet the eligibility criteria—which the study team decides, not us.

  • NCT06643728 is Lilly's Phase 2 study of bimagrumab and tirzepatide, alone or combined, in adults with obesity or overweight without type 2 diabetes. Its public Lilly page lists an enrollment goal of 252, a trial window from October 21, 2024 to January 2027, and completed enrollment, so it is closed to new participants.8
  • NCT05933499 is a separate Massachusetts General Hospital study examining tirzepatide and bimagrumab effects on body composition, insulin sensitivity, and bone. It was listed as recruiting at verification, with 63 participants planned and completion extending into 2029.12

Search the official registry directly rather than trusting any static list—including ours. Statuses change.

The RX Index Bimagrumab Evidence Ledger

Version 1.0 · Verified August 4, 2026

The RX Index Bimagrumab Evidence Ledger
TrialWhat it studiesPublic status at verificationEnrollmentCurrent date markerWhat the status means
NCT05616013 — BELIEVEIV bimagrumab, semaglutide, and combinations in adults with obesity or overweight without diabetesCompleted; peer-reviewed results published507 randomizedNature Medicine, March 2, 2026Published Phase 2 evidence exists. It is not an approval
NCT06643728Subcutaneous bimagrumab and tirzepatide, alone or combined, without type 2 diabetesCompleted enrollment252 goalListed trial window through January 2027The program continued after the separate diabetes-study withdrawal; no result should be assumed before publication
NCT05933499Tirzepatide and bimagrumab effects on body composition, insulin sensitivity, and boneRecruiting at verification63 plannedRegistry completion extends into 2029A separate academic study is open at listed sites; eligibility is determined by the study team
NCT06890611Relative bioavailability and formulation comparison of bimagrumabCompleted Phase 1125 participants listedCompleted in 2025Formulation work continued; it does not predict approval
NCT06901349Bimagrumab and tirzepatide in adults with obesity or overweight and type 2 diabetesWithdrawn before enrollment for stated strategic business reasons0 enrolledWithdrawn in 2025It produced no efficacy or safety result

Bimagrumab Trial Result Explorer

Download the versioned ledger (CSV)

Every row below is drawn from the server-rendered tables and sources on this page. Use the filters to isolate a trial, timepoint, regimen, or analysis.

Trial results and registry status — filtered view
TrialReferenceTimepointRegimenAnalysisWeight changeLean mass (DXA)Fat massVisceral fatWhat this supportsWhat this does not proveSource
2021 trialNCT03241602Week 48Bimagrumab onlyCompleters analysis-6.5% (vs placebo -0.8%)+3.6%-20.5%-26.9%A standalone bimagrumab signal for fat loss and weight loss in adults with type 2 diabetes.A strength benefit, or that an obesity (non-diabetes) population responds the same way; completers analysis only.JAMA Network Open 2021
2021 trialNCT03241602Week 48PlaceboCompleters analysis-0.8%-1.5%-0.5%-1.3%The placebo comparator for the 2021 trial; the 5.7-point gap is the trial's treatment signal.Anything about bimagrumab in people without type 2 diabetes.JAMA Network Open 2021
BELIEVENCT05616013Week 48CombinationTreatment-regimen estimand-16.4% (semaglutide -13.5%)Adding bimagrumab to semaglutide 2.4 mg improved weight loss by 2.9 percentage points in the primary-period estimand.The efficacy-level gap (5.4 pp); the treatment-regimen estimand accounts for discontinuation and adherence.Nature Medicine 2026 (BELIEVE)
BELIEVENCT05616013Week 48CombinationEfficacy estimand-20.2% (semaglutide -14.8%)Under full-adherence conditions the incremental benefit of the combination widened to 5.4 percentage points.A real-world (as-assigned) result; 74.4% of the 507 randomized participants completed the 48-week primary period.Nature Medicine 2026 (BELIEVE)
BELIEVENCT05616013Week 72Bimagrumab onlyEfficacy estimand-10.8%+2.5%-28.5%-45.1%High-dose bimagrumab alone produced substantial weight and fat loss while raising DXA lean mass at week 72.That the DXA 'lean mass' gain equals functional skeletal-muscle strength; no matching strength signal was demonstrated.Nature Medicine 2026 (BELIEVE)
BELIEVENCT05616013Week 72Semaglutide onlyEfficacy estimand-15.7%-7.4%-27.8%-35.8%The comparator arm: semaglutide 2.4 mg alone produced -15.7% weight loss but lost lean mass.That the lean-mass loss had a measurable functional consequence in this 52-week exploratory analysis.Nature Medicine 2026 (BELIEVE)
BELIEVENCT05616013Week 72CombinationEfficacy estimand-22.1%-2.9%-45.7%-58.2%The headline: 22.1% weight loss, a 84.9% rate of 15% or greater weight loss, and fat/VAT losses well beyond either arm alone.A personal forecast, an approval, safety in a large population, or a durable maintenance result after treatment ends.Nature Medicine 2026 (BELIEVE)
BELIEVENCT05616013Week 72CombinationDiscontinuation due to adverse eventsDropout due to adverse events was lower in the combination (5.3-12.5%) than with bimagrumab alone (14.0-21.4%).Preapproval-level safety; every arm discontinued at notable rates, and 507 randomized participants yielded a 74.4% primary-period completion rate.Nature Medicine 2026 (BELIEVE)
Development trackerNCT06643728n/aCombinationRegistry statusLilly's Phase 2 bimagrumab + tirzepatide program (enrollment goal 252) had completed enrollment at verification.Any result before data are posted or published; the listed trial window runs through January 2027.ClinicalTrials.gov + Lilly
Development trackerNCT05933499n/aCombinationRegistry statusAn independent Mass General study of tirzepatide + bimagrumab on body composition, insulin sensitivity, and bone was recruiting at verification.That any participant qualifies; eligibility is determined by the study team, and enrollment completion is not a result.ClinicalTrials.gov
Development trackerNCT06890611n/an/aRegistry statusLilly completed a Phase 1 formulation and relative-bioavailability study (125 participants listed).Whether Lilly starts Phase 3, submits, or commercializes; formulation work is not an approval signal.ClinicalTrials.gov
Development trackerNCT06901349n/an/aRegistry statusThe separate Lilly bimagrumab + tirzepatide diabetes study was withdrawn before enrollment for stated strategic business reasons.Efficacy or safety; it produced no result, and it does not halt the NCT06643728 program.ClinicalTrials.gov

Showing 12 of 12 results. All figures are as reported in the cited sources and were verified August 4, 2026. Bimagrumab is not FDA-approved; no result here is medical advice.

### You can't get bimagrumab. You can still get a plan. Bimagrumab is not an available treatment and has no verified launch date. Your options today depend on things a headline can't answer—your state, your insurance, whether you want an FDA-approved or compounded medication, and what you can afford. Get your personalized GLP-1 action plan → Takes about 2 minutes. No cost. The RX Index's Find My GLP-1 Path tool matches you to treatment paths with source-verified pricing.


How much weight did people lose on bimagrumab?

Two human trials have published weight results. In a 2021 study of 75 adults with type 2 diabetes, bimagrumab alone was associated with 6.5% average weight loss at 48 weeks. In the larger 2026 BELIEVE trial of 507 adults without diabetes, high-dose bimagrumab alone was linked to 10.8% weight loss at week 72, semaglutide 2.4 mg to 15.7%, and the two combined to 22.1%.31

Those aren't the same study, the same patients, or the same analysis. Anyone stacking them into one tidy story is doing you a disservice. Here they are side by side, with the fine print attached.

The two published bimagrumab trials, normalized

The two published bimagrumab trials, normalized
2021 trial (JAMA Network Open)BELIEVE—week 48 (Nature Medicine)BELIEVE—week 72
Who75 adults with type 2 diabetes, BMI 28–40507 adults with obesity or overweight plus a complication, no diabetesExtension of the same Phase 2 study
TreatmentBimagrumab 10 mg/kg IV every 4 weeks, or placeboBimagrumab 10 or 30 mg/kg, semaglutide 1.0 or 2.4 mg, combinations, or placeboSelected arms continued through the extension
Analysis usedEfficacy analysis limited to participants who completed the full regimenTreatment-regimen estimandEfficacy estimand—all week-72 analyses post hoc
Weight change−6.5% vs −0.8% placeboBimagrumab −5.6% to −8.6% · Semaglutide −9.8% to −13.5% · Combination −12.0% to −16.4% · Placebo −3.5%Bimagrumab −10.8% · Semaglutide −15.7% · Combination −22.1%
Fat mass−20.5% vs −0.5%Combination arms produced the largest reductions−28.5% · −27.8% · −45.7%
Lean mass+3.6% vs −0.8%Bimagrumab +1.0% to +1.1% · Semaglutide −4.7% to −6.9% · Combination −0.8% to −2.3%+2.5% · −7.4% · −2.9%
Big limitationSmall; 58 of 75 completed; sex imbalance; no effect on grip strengthStill Phase 2; nominal comparisons without multiplicity adjustmentNo continuing true placebo through the extension; post hoc; no multiplicity adjustment

Sources: Heymsfield et al., JAMA Network Open 2021;4(1):e2033457 · Heymsfield et al., Nature Medicine 2026;32(3):869–882 (BELIEVE, NCT05616013).

What else BELIEVE measured

Weight is the headline. These numbers are arguably more interesting.

What else BELIEVE measured
Week-72 outcome (efficacy estimand)Bimagrumab 30 mg/kgSemaglutide 2.4 mgBoth, high dose
Body weight−12.0 kg (−10.8%)−16.5 kg (−15.7%)−24.2 kg (−22.1%)
Total body fat−28.5%−27.8%−45.7%
DXA-measured lean mass+2.5%−7.4%−2.9%
Modeled share of weight reduction attributable to fat100%75.6%92.2%
Estimated visceral adipose tissue−45.1%−35.8%−58.2%
Reached 15% or more weight loss21.8%51.8%84.9%
LDL cholesterol+17.6%−8.9%+0.1%

Two things jump out.

The visceral-fat number is remarkable. Bimagrumab alone reduced estimated visceral adipose tissue by 45.1%—more than semaglutide's 35.8%—while producing less total weight loss. That pattern is consistent with the biological rationale that made the activin pathway interesting in obesity research.145

And the LDL number is a real flag. LDL cholesterol rose 17.6% with high-dose bimagrumab alone at week 72. It fell 8.9% with semaglutide 2.4 mg and was nearly unchanged, at +0.1%, in the high-dose combination. Nobody should report the body-composition upside without reporting that result too.1

The trade nobody mentions

Look at that row again: 21.8% of people on high-dose bimagrumab alone reached at least 15% weight loss. On semaglutide 2.4 mg, 51.8% did.

The most favorable DXA body-composition pattern in the three high-dose week-72 groups did not come with the biggest weight loss.

Bimagrumab alone had a modeled fat-loss index of 100%: average fat-mass reduction exceeded average total-weight reduction because lean mass increased. But less total weight came off than with semaglutide. If your priority is the number on the scale, bimagrumab monotherapy produced the weaker result in this analysis. If your priority is the composition of that change, its DXA result was more favorable.

That's the actual trade. It also explains why combining an activin-pathway drug with an incretin is a central development idea: one may add fat-directed body-composition effects while the other adds greater total weight loss. Whether that becomes a safe, approved, worthwhile treatment is still unanswered.


What does the 22.1% result actually mean?

The 22.1% figure was a modeled average for people assigned to high-dose IV bimagrumab plus semaglutide 2.4 mg, measured at week 72 under the trial's efficacy estimand, in an analysis the authors labeled post hoc. It is a strong Phase 2 signal. It is not a guaranteed personal result, an approved-product claim, or a prediction of what happens in routine medical practice.1

Here's the thing about that number: it's real, it's published, and it's been repeated across the internet with almost none of the context that determines what it means.

We built this table so you can check any bimagrumab claim you see against what the study actually supports.

The bimagrumab reality check

The bimagrumab reality check
What you'll readWhat the study actually saysWhat it supportsWhat it does not support
“Bimagrumab caused 22.1% weight loss”That was high-dose IV bimagrumab plus semaglutide 2.4 mg, at week 72, under the efficacy estimandA strong Phase 2 signal for the combinationNot a bimagrumab-alone result; not an approved dose; not your predicted result
“Bimagrumab alone caused 10.8% weight loss”High-dose monotherapy, modeled average, week 72Bimagrumab has a standalone human obesity signalDoes not establish a commercial dose or routine-practice effect
“It prevents muscle loss”Week-72 DXA lean mass: +2.5% bimagrumab, −7.4% semaglutide, −2.9% combinationThe combination preserved substantially more lean mass than semaglutide aloneThe combination still lost 2.9%; DXA lean mass is not identical to skeletal muscle
“All the weight lost was fat”The modeled fat-loss index for high-dose monotherapy was 100%Average body-composition change was strongly fat-directedDoes not mean every participant lost only fat
“It builds muscle and makes you stronger”DXA lean mass rose with bimagrumabA measurable body-composition effectBroad improvement in objective strength was not demonstrated
“The results are definitive”All week-72 analyses were post hoc with no multiplicity adjustmentEnough to justify further studyNot Phase 3 confirmation
“The drug is safe”91.1%–98.2% of active-treatment participants had a treatment-emergent adverse event; no deaths were reportedA substantial Phase 2 safety datasetDoes not establish the final safety, contraindication, or monitoring profile
“Lilly stopped bimagrumab”One diabetes study was withdrawn before enrollment; a separate 252-participant study continuedThe withdrawal report was realThe public program did not end, and the withdrawn study generated no safety result
“You can get it now”Investigational, Phase 2Trial participation where a study is recruiting and the person qualifiesNo routine prescription; no approved commercial product; no verified price

What's an “estimand,” and why should you care?

Because the same trial can produce two different numbers depending on the question the analysis is built to answer, and the gap is bigger than most people would guess.

An estimand is the precise treatment effect a statistical analysis is trying to estimate. BELIEVE used two.

The treatment-regimen estimand asks about the effect of assignment to treatment while accounting for discontinuation and adherence under its specified strategy. The efficacy estimand asks about the expected treatment effect under the hypothetical condition that participants adhere to treatment and do not discontinue. It is not simply an average of “people who finished.”

Neither is wrong. They answer different questions.

But look what happens to the same high-dose comparison at week 48:

What's an “estimand,” and why should you care?
AnalysisHigh-dose combinationSemaglutide 2.4 mgIncremental difference
Treatment-regimen estimand−16.4%−13.5%2.9 percentage points
Efficacy estimand−20.2%−14.8%5.4 percentage points

The apparent incremental benefit of adding bimagrumab nearly doubles depending on which estimand you read.

Hold onto that. It is the clearest reason not to reduce BELIEVE to one number.

Does 22.1% mean you'd lose 22.1%?

No. It is a modeled group average, not a personal forecast. Individual responses varied, and only 74.4% of the 507 randomized participants completed the 48-week primary period.

We're not going to build you a bimagrumab weight-loss calculator. Projecting a personal result from an unapproved Phase 2 average would be dressing up a guess as a tool.


Did bimagrumab really save people's muscle?

On DXA lean-mass measurements, the signal was clear. At week 72, lean mass rose 2.5% with high-dose bimagrumab, fell 7.4% with semaglutide alone, and fell 2.9% with the combination. But “lean mass on a DXA scan” is broader than skeletal muscle, and the trial did not show a matching broad improvement in objective strength. More lean mass on a scan and stronger in real life are not yet the same claim.1

This section is where most coverage overreaches, so we're going to be careful.

Lean mass is not the same as muscle

A DXA scan splits your body into three broad compartments: fat, bone mineral, and everything else. That third compartment is “lean mass.” It includes skeletal muscle—but also organs, connective tissue, body water, and other nonfat soft tissue.

The BELIEVE authors say this themselves. Earlier bimagrumab studies used MRI to measure regional skeletal-muscle volume more directly. BELIEVE used DXA, where muscle was contained within the broader lean-mass measurement. The authors specifically called for future studies using MRI and physical-function measures in populations at risk.1

Here's a quick guide, because these terms get swapped around constantly:

Lean mass is not the same as muscle
TermWhat it actually measuresWhat it is not
DXA lean massNonfat, non-bone-mineral soft tissueDirectly measured skeletal muscle
Appendicular lean massLean mass in the arms and legs—a closer proxyProof of muscle quality or function
MRI muscle volumeAnatomical muscle volume in the imaged regionA whole-body measurement unless the protocol supports that claim
Grip strengthA functional strength testA measure of total muscle quantity
Physical-function questionnaireA participant-reported measure of capabilityAn objective strength test

Did the combination stop lean-mass loss completely?

No. And this gets stated wrong constantly.

The high-dose combination group still lost 2.9% of DXA-measured lean mass at week 72. That's substantially less than semaglutide's 7.4%—about 61% less relative loss—but it isn't zero.

“Preserved much more lean mass” is accurate. “Prevented all muscle loss” is not.

Did people actually get stronger?

Mostly, no—and this is the honest gap in the whole muscle-preservation story right now.

  • In the 2021 trial, there was no treatment effect on handgrip strength.3
  • In BELIEVE at week 48, SF-36 self-reported physical-function changes were not significantly different from placebo across groups under the treatment-regimen estimand.1
  • Grip strength was significantly better than placebo in one of nine treatment groups—bimagrumab 30 mg/kg plus semaglutide 1.0 mg, at 4.8 kg versus 1.7 kg. All remaining groups were similar to placebo.1

The authors offer a fair explanation: the trial enrolled a broad population, and specific groups with lower baseline function may respond differently. They also state that the study was too small for reliable age- and sex-subgroup conclusions.

But as of today, a broad functional payoff has not been demonstrated. If someone tells you bimagrumab makes people stronger, ask them which trial showed it.

What about bone?

BELIEVE did not show that adding bimagrumab prevented hip bone-density loss. At week 48, total-hip bone mineral density fell 2.1% with semaglutide 2.4 mg, 2.0% with bimagrumab 10 mg/kg plus semaglutide 1.0 mg, and 2.2% to 2.3% in the two combination groups containing bimagrumab 30 mg/kg, compared with 0.8% on placebo. Changes in total-body and lumbar-spine bone density were 1.1% or less across groups.1

So in the published human obesity trial, the high-dose combinations preserved more DXA lean mass but did not prevent the measured decline in total-hip bone density. Reduced mechanical loading during substantial weight loss is one possible explanation discussed in the paper, but the trial does not prove one cause.

If bone health is already a concern, this is worth raising with your clinician no matter which weight-management medication you use.

Related: we maintain a source-normalized GLP-1 Lean Mass Ledger showing how body-composition outcomes were measured and reported across published trials.


What are bimagrumab's side effects?

The most common adverse events reported with bimagrumab in BELIEVE were muscle spasms—usually described as cramps—plus diarrhea and acne. The bigger issue is tolerability overall: 14.0% to 21.4% of participants in the bimagrumab-only groups stopped treatment because of adverse events, compared with 3.6% on placebo. Only 74.4% of the 507 randomized participants completed the 48-week primary period.1

Now the damaging admission, and we're putting it before the good part on purpose.

As many as one in five people quit a bimagrumab-only arm

That's the number. Depending on dose, 14.0% to 21.4% of participants assigned to bimagrumab alone stopped treatment because of adverse events. On placebo it was 3.6%.

For comparison across the trial:

As many as one in five people quit a bimagrumab-only arm
GroupDiscontinued treatment because of adverse events
Bimagrumab-only groups14.0%–21.4%
Combination groups5.3%–12.5%
Semaglutide-only groups3.6%–8.8%
Placebo3.6%

This matters more than it looks. Remember the two estimands? The 22.1% week-72 result comes from an efficacy estimand estimating what would be expected under the hypothetical condition that participants adhered to treatment and did not discontinue. When discontinuation differs across groups, that question and the treatment-regimen question can produce meaningfully different answers.

So here's the plain version: bimagrumab does not look like a drug you'd hand to everyone. The published data show a body-composition effect and a real tolerability cost. FDA-approved obesity medications available now have larger later-stage and post-approval evidence bases, established prescribing information, and defined contraindications. Bimagrumab has none of those yet.

The possible future case is narrower: a person for whom loss of lean tissue has unusual clinical consequences may accept a different trade. BELIEVE did not prove that case in older adults, people with frailty, or people with sarcopenic obesity. It showed enough to make that question worth testing.

What the adverse events actually were

What the adverse events actually were
Reported commonly with bimagrumabReported commonly with semaglutideCombination groups
Muscle spasms or crampsNauseaEvents reflecting both treatment patterns
DiarrheaDiarrheaAll six nausea-related discontinuations occurred here
AcneConstipationMuscle, skin, and gastrointestinal events
Laboratory changes described belowFatigueAdded tolerability burden remains under study

There's a real irony in the top item. The drug being studied to preserve lean tissue caused muscle spasms often enough that five participants in the bimagrumab-monotherapy groups stopped treatment because of them. Four additional discontinuations across bimagrumab-containing groups were attributed to acne.1

Similar muscle-spasm patterns have been reported with other interventions affecting myostatin or activin signaling, but BELIEVE alone cannot establish how much of this is a pathway-wide class effect.

Serious events, reported completely

We're going to list these plainly rather than bury them, because if you find them somewhere else after reading this page, we've failed.

  • Serious adverse events were reported in 8.8%–12.5% of bimagrumab participants, 1.8%–10.7% of semaglutide participants, 3.6%–9.1% of combination participants, and 3.6% of placebo participants.
  • No deaths were reported.
  • Three serious pancreatitis events occurred during the 48-week primary period—one each in the placebo, bimagrumab 10 mg/kg, and semaglutide 1.0 mg groups. The investigators described pancreatitis as infrequent and balanced across groups.
  • Four participants reported basal- or squamous-cell skin carcinoma during the primary period, all in single-drug groups. Two additional basal-cell carcinomas were reported during the extension. The trial reports those events; it does not establish that bimagrumab or semaglutide caused them.1

“No deaths” is not the same as “safe.” A 507-person Phase 2 study is not large or long enough to define an eventual commercial safety profile or detect every uncommon risk.

Laboratory changes worth knowing

Bimagrumab-containing groups showed mean increases in alkaline phosphatase and creatine kinase, transient increases in ALT and AST, and decreases in magnesium that remained within the normal range. Lipase rose transiently with bimagrumab and rose and remained elevated with semaglutide treatment.1

And the LDL cholesterol finding from earlier: up 17.6% with high-dose bimagrumab alone at week 72, down 8.9% with semaglutide 2.4 mg, and nearly unchanged at +0.1% with the high-dose combination.

The trial authors wrote that high IV loading and peak exposure may have contributed to early laboratory changes and suggested that subcutaneous dosing may attenuate some effects. That's a hypothesis supported by formulation work, not an established clinical advantage.113

What's still unknown

Long-term safety. An approved contraindication list. Drug interactions. Safety in older or frail people. Whether body-composition changes reduce falls, disability, or fractures. What happens after treatment stops. The safety and effectiveness of whatever dose and formulation might eventually move forward.

That's a long list. It's normal for Phase 2. It's also why nobody can prescribe an approved bimagrumab product today.


Did Eli Lilly stop developing bimagrumab?

No—not based on the public record. Lilly withdrew one planned Phase 2 study of bimagrumab with tirzepatide in people who had both obesity and type 2 diabetes for stated “strategic business reasons,” before a single participant enrolled. A separate 252-participant Phase 2 study in adults without diabetes continued and completed enrollment, and a formulation study was completed.14813

If you saw a headline in 2025 saying Lilly halted a bimagrumab trial, that headline was accurate. It just wasn't the whole picture, and the difference is easy to miss.

Two different studies:

Did Eli Lilly stop developing bimagrumab?
The one that was called offThe one that continued
Trial IDNCT06901349NCT06643728
WhoAdults with obesity or overweight and type 2 diabetesAdults with obesity or overweight, without diabetes
Public statusWithdrawn for “strategic business reasons”Phase 2; enrollment complete
ParticipantsZero enrolled252 enrollment goal
ResultNone—no participant data were generatedPublic trial window runs through January 2027; no result should be assumed before release

Because nobody enrolled in the withdrawn study, it produced no efficacy result and no safety result. There is nothing there to interpret.

Did “strategic reasons” mean there was a safety problem? The public registry does not say so, and a study with zero participants could not have generated a study safety signal. It would also be dishonest to claim we know every factor behind Lilly's internal decision. The public conclusion is narrower: the stated reason was strategic, no participant result exists, and other bimagrumab work continued.

Lilly also completed NCT06890611, a Phase 1 study comparing bimagrumab formulations and administration approaches. That shows formulation work continued. It does not predict whether Lilly will start Phase 3, seek approval, or commercialize the drug.13

The fair conclusion: one study stopped before enrollment; the publicly listed non-diabetes and formulation programs continued. Continued development is not an approval signal. It is evidence that “Lilly abandoned bimagrumab” is too broad.


When could bimagrumab actually be available?

There is no announced approval date, launch date, or commercial price. The most advanced current public obesity program remains Phase 2, and no public Phase 3 bimagrumab obesity trial was identified as of August 4, 2026.2 That means no honest page can give you a reliable year when a prescription will become available.8

The sequence still ahead could include:

  1. Completion and analysis of the current Phase 2 programs.
  2. A sponsor decision about whether the evidence justifies further development.
  3. One or more later-stage trials designed with regulators.
  4. Manufacturing, safety, and formulation work.
  5. A regulatory submission, if the later-stage program succeeds.
  6. FDA review and a decision.

Every step can change, take longer than expected, or stop. A trial-end date is not a launch date.

What has to be true before a launch claim is real?

Here is the launch-readiness check the public record supports today. It separates evidence that exists from milestones that have not happened publicly.

What has to be true before a launch claim is real?
MilestoneVerified status on August 4, 2026What it means
Peer-reviewed obesity resultsYes. BELIEVE is published, along with the earlier 2021 trialBimagrumab has a human Phase 2 efficacy and safety signal
Current bimagrumab–tirzepatide Phase 2Enrollment complete. Results were not publicly posted or published at verificationThe next major obesity dataset is still pending
Public Phase 3 obesity registrationNone identified in ClinicalTrials.gov or Lilly's public trial program2No public registrational obesity program can be used to forecast a launch
Sponsor-announced FDA submissionNone identified in the public sources reviewed2There is no public regulatory-review clock to count down
Approved dose, formulation, or routeNoneBELIEVE's IV regimen and current subcutaneous studies do not define a commercial product
Approved prescribing informationNoneNo final indication, contraindication list, monitoring plan, or patient population exists
Commercial list price or insurance policyNoneAny patient-price estimate is speculation

That table is the honest answer to timing. The public record supports saying the program is active and remains in Phase 2. It does not support saying bimagrumab will launch in 2027, 2028, or “soon.”1810

The estimand comparison still matters for whatever comes next. At week 48, adding high-dose bimagrumab to semaglutide 2.4 mg produced an incremental difference of 2.9 percentage points under the treatment-regimen estimand and 5.4 points under the efficacy estimand. That is not an approval threshold. It shows that any later-stage program will need a clearly prespecified analysis strategy and a convincing answer to treatment discontinuation.

Is January 2027 an approval date?

No. January 2027 is the current listed end of NCT06643728's trial window. Data cleaning, analysis, sponsor decisions, later-stage trials, a submission, and regulatory review are separate events.8

Treat any page giving you a precise bimagrumab launch year as a forecast, not a verified fact.

What will bimagrumab cost?

Nobody knows, and anyone quoting a patient price is making it up. There is no approved product, manufacturer list price, insurer coverage policy, or commercial dose. Monoclonal antibodies can be complex to manufacture and administer, but turning that general fact into a bimagrumab price would be speculation dressed as information.

### The drug bimagrumab was measured against may already be available to you BELIEVE's high-dose comparison arm used semaglutide 2.4 mg—a dose of an FDA-approved medication. The exciting combination number exists on top of a treatment path people can access now when medically appropriate. If you've been holding off while you wait for bimagrumab, the first useful question isn't which future drug wins. It's whether your insurance covers an approved option today. Ro's free checker currently reports coverage for the Ozempic® pen, Wegovy® pen, and Zepbound® pen. It does not currently check Foundayo™ pill, Wegovy® pill, or Zepbound® KwikPen® coverage. Ro Body membership is $39 for the first month, then $149 month to month or as low as $74 per month with a 12-month plan paid upfront; medication is charged separately. Verified August 4, 2026.1516 Check your insurance coverage for an FDA-approved GLP-1 → Affiliate link. Eligibility, coverage, prior authorization, medication choice, and prescription decisions are not guaranteed. Paying cash instead? Compare current manufacturer, insurance, Medicare, and self-pay channels in our GLP-1 Price & Access Tracker before you commit.

What we verified before using that provider handoff

Ro appears here as a current access path for FDA-approved treatment—not as evidence about bimagrumab and not as a guaranteed coverage result. We checked the live insurance scope and the membership fee separately so the provider claim, the verified fact, and the limitation stay visible.1516

What we verified before using that provider handoff
Current Ro-stated factWhat we verified on August 4, 2026Limitation that changes the decision
Free GLP-1 insurance checkRo's live pricing page says it checks Ozempic®, Wegovy®, and Zepbound® autoinjector-pen coverageIt does not currently check Foundayo™ pill, Wegovy® pill, or Zepbound® KwikPen® coverage
Ro Body membership starts at $39$39 for the first month; $149 month to month; as low as $74/month with a 12-month plan paid upfrontMedication is charged separately, and eligibility, prescribing, prior authorization, and insurance approval are not guaranteed
Insurance support is includedRo says the program includes insurance-concierge and prior-authorization supportSupport can handle paperwork; it cannot make a plan cover a drug or guarantee a favorable out-of-pocket price

Can you buy bimagrumab online?

There is no approved bimagrumab product to buy online. Scientific suppliers sell research-grade antibody reagents in milligram quantities and label them for research use only—not for patients. In the United States, FDA says biological products are not eligible for the drug-compounding exemptions in sections 503A or 503B, so “compounded bimagrumab” is not a lawful substitute for an approved biologic.1718

We're not going to lecture you. We're going to show you the scale difference and let the arithmetic do the work.

The trial-scale arithmetic

BELIEVE's average starting body weight was 107.5 kg. Its high-dose bimagrumab regimen used 30 mg/kg; the lower regimen used 10 mg/kg.1

For an average participant in that trial:

  • High trial amount: 107.5 kg × 30 mg/kg = 3,225 mg per infusion
  • Lower trial amount: 107.5 kg × 10 mg/kg = 1,075 mg per infusion
  • Representative exact-product research-reagent listing: 5 mg
  • One 5 mg vial equals 0.16% of the high trial amount
  • It would take 645 five-milligram vials to equal the high trial amount
  • It would take 215 five-milligram vials to equal the lower trial amount
  • The 2021 study capped one infusion at 1,200 mg, equal to 240 five-milligram vials318

This is not a dosing guide. It is a scale check using published trial arithmetic. The trial used a manufactured investigational biologic, prepared and administered under a protocol as a 30-minute IV infusion at a clinical site. A research reagent in a catalog is not the clinical-trial product and cannot be converted into one by buying more units.

What research suppliers are actually selling

Legitimate scientific suppliers describe these products as research-grade reference antibodies or biosimilars for laboratory work. Representative listings explicitly state “research use only” and “we do not sell to patients.” The exact bimagrumab listing we checked offered 1 mg and 5 mg packages, but the intended uses are laboratory research—not self-administration.18

That label does not establish:

  • FDA-approved manufacturing for human use
  • Clinical identity or comparability to Lilly's investigational product
  • Sterility for infusion
  • An approved concentration, excipient, or formulation
  • Safe storage and handling for patient treatment
  • A lawful prescription pathway

A consumer-facing seller may repeat the molecule's name. That does not make its product an approved or clinically interchangeable version of bimagrumab.

Why compounding is not a workaround in the United States

You may know that some conventional drugs can be compounded under sections 503A or 503B when legal requirements are met. Bimagrumab is a biological product—a large recombinant monoclonal antibody—rather than a conventional small-molecule drug or peptide product.

FDA's current answer is direct: biological products are not eligible for the compounded-drug exemptions under sections 503A and 503B, and federal law does not provide a pathway to market a biologic prepared outside an approved biologics license application. FDA describes limited enforcement policies for mixing, diluting, or repackaging certain approved biological products; that is not a route for creating an unapproved bimagrumab product from scratch.17

If someone offers “compounded bimagrumab” to a U.S. patient, the label itself should stop the conversation. There is no FDA-approved bimagrumab biologic to compound, and the statutory drug-compounding exemptions do not cover biological products.


What else is being tested to preserve lean mass during GLP-1 weight loss?

Bimagrumab is one of several investigational drugs being tested for better body composition during obesity treatment. The approaches are not interchangeable: some block myostatin or activin signaling, one is an oral selective androgen receptor modulator, and the early studies differ sharply in population, duration, evidence quality, weight loss, lean-mass change, and tolerability. None is FDA-approved for preserving muscle during GLP-1 treatment.

This is a selected comparison of the programs with public human obesity data or an active obesity study—not a claim that every experimental muscle drug belongs in one race.

The muscle-preservation pipeline on the same columns

The muscle-preservation pipeline on the same columns
Investigational drugTarget or approachObesity evidence verified by August 4, 2026Total-weight signalLean-mass or body-composition signalEvidence maturityWhat a reader should not assume
BimagrumabAntibody blocking ActRIIA and ActRIIBBELIEVE: 507 randomized; peer-reviewed Phase 2. Separate bimagrumab–tirzepatide Phase 2 completed enrollmentWeek 72: −15.7% with semaglutide 2.4 mg vs −22.1% with the high-dose combination under the efficacy estimandWeek 72 DXA lean mass: −7.4% with semaglutide vs −2.9% with the high-dose combination; +2.5% with bimagrumab alonePeer-reviewed Phase 2 plus active registry programNo approved dose, route, price, launch date, or Phase 3 result
Trevogrumab with or without garetosmabAnti-myostatin antibody, with optional anti-activin A antibodyRegeneron COURAGE: 599 randomized; company-reported 26-week Phase 2 resultsSemaglutide alone −10.6%; semaglutide + higher-dose trevogrumab −11.1%; triple combination −13.4%Lean mass: −6.5%, −3.8%, and −2.0%, respectively; triple combination fat mass −27.1%Sponsor topline; not yet a peer-reviewed full paper at verificationThe triple regimen also had higher treatment discontinuation and two deaths; Regeneron said no causal association was identified, but the full peer-reviewed context still matters
ApitegromabSelective inhibitor of latent myostatin activationEMBRAZE: 102 participants; 24-week randomized Phase 2 proof-of-concept published in Nature MedicineMean weight loss was similar: 11.2 kg with apitegromab + tirzepatide vs 12.5 kg with tirzepatide + placeboThe combination preserved 1.9 kg more lean mass; no notable between-group improvement in physical function was establishedPeer-reviewed Phase 2 proof of conceptLean-mass preservation did not produce more total weight loss in this study
EnobosarmOral selective androgen receptor modulatorQUALITY: 168 older adults; results publicly reported by Veru. PLATEAU: more than 200 adults age 65+ with BMI ≥35; enrollment completed in July 2026QUALITY showed similar short-term total weight loss overall; PLATEAU is testing incremental weight loss through 68 weeksVeru reported less lean-mass loss and better selected physical-function results in QUALITY; the longer PLATEAU test remains ongoingCompany-reported QUALITY; current Phase 2b PLATEAUCompany topline is not the same evidentiary level as a full peer-reviewed article, and the PLATEAU result is not known yet
Taldefgrobep alfaMyostatin–activin pathway inhibitorBiohaven Phase 2 proof-of-concept obesity study completed enrollment; company expected topline data in the second half of 2026No public obesity result at verificationNo public obesity result at verificationEnrolled Phase 2; result pendingAn active program is not evidence that it works

Sources and evidence labels are attached below. Regeneron, Veru, and Biohaven figures are sponsor-reported unless a peer-reviewed paper is named.19202122

The important split is “more weight loss” versus “different weight loss”

These programs are often described as though they have one job: save muscle. The trials are testing at least two different commercial and clinical ideas.

One idea is additive weight loss. BELIEVE's high-dose bimagrumab combination and Regeneron's reported triple combination reduced more total weight than their GLP-1 comparison arms in their respective studies. If confirmed, the added drug is not only changing what comes off; it is adding to how much comes off.

The other idea is tissue selectivity. Apitegromab preserved more lean mass while total weight loss remained similar to tirzepatide alone. That may still matter clinically, but it creates a different regulatory and value question: is the composition or functional benefit large and meaningful enough to justify another drug, another safety profile, and another cost?

Neither job is automatically better. A person with low muscle reserve may care more about strength, mobility, and independence than an extra point on the scale. A younger person primarily seeking more weight loss may make the opposite trade. The trials have not yet shown who benefits enough to justify the added burden.

Source maturity matters as much as the headline

The bimagrumab and apitegromab obesity results now have peer-reviewed full papers. The Regeneron COURAGE numbers, Veru QUALITY claims, and Biohaven timeline were company-reported at verification. Sponsor releases can be useful and may be accurate, but they are selected communications, not substitutes for a full methods section, complete adverse-event tables, prespecified analysis plan, and peer review.

That is why the table labels the evidence source instead of flattening every number into one leaderboard.

Related: follow phase changes and readout dates in our GLP-1 Clinical Trials Tracker.


What actually protects lean mass during weight loss right now?

The things with current clinical support are less exciting than an experimental antibody: adequate nutrition, enough protein for your situation, and resistance training that is safe and realistic for you. BELIEVE added lifestyle counseling to every group—including a protein target of at least 1.2 g/kg/day and at least 150 minutes of weekly physical activity—so bimagrumab was tested on top of that foundation, not instead of it.123

This is the most useful section on the page, so read it twice.

Every BELIEVE group received the same lifestyle framework. Semaglutide 2.4 mg still showed a 7.4% modeled decline in DXA-measured lean mass by week 72, while the high-dose combination showed a 2.9% decline. That does not prove every participant met the protein or activity target, and 150 minutes of general activity is not the same as a supervised resistance-training program. It does show that the drug comparison was not made against a “do nothing” lifestyle arm.

So protein and training are the foundation. They're also not the whole answer. Both halves are true, and most coverage tells you only one.

Protein takes deliberate planning when appetite falls

BELIEVE found that protein rose as a share of calories more in the bimagrumab and placebo groups than in the semaglutide and combination groups. That fits a practical problem people report on appetite-suppressing treatment: when total intake drops, protein can drop with it unless meals are planned around it.1

A joint clinical advisory from major obesity and nutrition organizations recommends assessing nutritional risk, prioritizing adequate protein, and pairing nutrition with strength training during GLP-1 therapy. It does not create one universal protein prescription for every person.23

We're not going to publish one number as though it fits everybody. Kidney disease, frailty, pregnancy, eating-disorder history, allergies, food access, and other medical conditions can change what is appropriate. The right target belongs in a conversation with a qualified clinician or dietitian who knows your situation.

Resistance training is the signal, not an optional extra

General movement matters. Resistance training gives the body a more specific reason to retain strength and muscle during an energy deficit.

That does not mean everyone needs a bodybuilding program. For one person, it may mean progressive weight training. For another, supervised physical therapy, resistance bands, sit-to-stand work, or a program built around joint disease, balance, or mobility limits. The safest useful program is the one you can perform consistently without creating a new problem.

The pace and quality of weight loss matter

Lean-tissue change depends on more than the medication name. Baseline muscle reserve, age, rate and magnitude of weight loss, total energy intake, protein intake, activity, illness, and measurement method all affect the result.

That is a real reason to work with a prescriber who manages treatment rather than only refilling it. “More weight loss, faster” is not automatically the best outcome if appetite suppression becomes so strong that nutrition, hydration, function, or tolerability deteriorates.

Measure more than the scale

A scale tells you total mass. It does not tell you whether a change came from fat, lean tissue, fluid, or a mixture.

Depending on your risk and access, a clinician may use:

  • Changes in strength or physical function
  • Waist measurement and weight trend
  • Nutrition and symptom review
  • DXA or another body-composition method when the result would change care
  • Simple functional markers, such as how easily you rise from a chair, climb stairs, carry groceries, or perform your normal training

Consumer body-composition scales estimate rather than directly measure tissue compartments. Their trend may be useful under consistent conditions, but a decimal on the screen is not the same as a DXA or MRI measurement.

Bring the concern into the appointment

“I'm losing weight, but I don't want to lose strength or function” is a legitimate treatment question. Ask what your clinician is monitoring, what would trigger a dose or nutrition change, and whether your age, baseline muscle reserve, or rate of loss changes the plan.

Bimagrumab cannot solve that problem for you today. A better current plan can still take it seriously.


Who might bimagrumab matter for if later trials confirm the benefit?

The strongest future case is likely to be people for whom losing lean tissue has unusually high consequences—older adults, people with low muscle reserve, or people at risk of mobility loss. The case is weaker for a younger healthy adult who mainly wants faster scale loss, because bimagrumab alone produced less total weight loss than semaglutide in BELIEVE and the studied IV regimen added a clinic-based treatment burden.

That's our editorial judgment based on the evidence above, not a proven indication. BELIEVE was not designed or large enough to establish a definitive age-, frailty-, or sarcopenia-specific benefit, and most objective function outcomes did not separate broadly from placebo.1

Where you fit

Where you fit
If you are...What bimagrumab means for youWhat to do now
On a GLP-1 and worried about lean massIt is not an available add-on. The published body-composition signal is relevant, but it does not create a prescription optionDiscuss nutrition, resistance training, pace, symptoms, and function at your next clinical check-in
Considering treatment and thinking about waitingThere is no verified launch date and no public Phase 3 obesity trialDo not defer needed care solely for an investigational product. Compare available treatment paths instead
Older or already low on muscle reserveThis is one of the groups for whom the research question may matter most, but direct proof is still missingAsk about strength, fall risk, nutrition, exercise, and whether body-composition or functional monitoring would change care
Being offered bimagrumab by a sellerThere is no approved patient product. Research reagents are not a treatmentDo not self-administer it. Use the trial-scale and regulatory facts above
Looking for muscle gain or performance enhancementThe obesity trials do not establish a safe performance useWrong drug, wrong evidence, and no approved product
A clinician or researcherThe live questions are estimand sensitivity, tolerability, functional benefit, route, and later-stage confirmationRead the primary paper, supplement, registries, and future full publications—not only topline coverage

### Does the first row sound like your situation? You do not need to choose a provider from a generic list. The right treatment path changes with your state, insurance, medication preference, health history, and budget. Find the GLP-1 path that fits your situation → Free. About 2 minutes. This tool provides an educational match, not a diagnosis or prescription.


What are people actually asking about bimagrumab?

There are no legitimate bimagrumab customer reviews because there is no approved commercial product or commercial patient program. The public human evidence comes from clinical studies. Public discussions are still useful for identifying the questions people are trying to answer, but they are not evidence of efficacy, safety, product identity, or access.

We are not going to manufacture a testimonial module for a drug nobody can buy. These are the three recurring questions underneath the hype.

“Isn't the lean-mass loss just from eating less protein?”

Nutrition is part of it. BELIEVE gave every group protein and activity counseling, and the semaglutide groups still showed larger DXA lean-mass reductions than the bimagrumab-containing comparison groups. That does not prove perfect adherence or erase the role of diet and training. It shows that the treatment signal remained in a trial where lifestyle support was part of the protocol.1

“Did Lilly stop it?”

No—not the whole program. Lilly withdrew one planned diabetes-population study before enrollment for stated strategic business reasons. A separate Phase 2 study without diabetes completed enrollment, and a formulation study was completed. That is continued development, not proof of acceleration or eventual approval.81314

“Can you get it yet?”

Not as an approved prescription. One academic trial was recruiting at verification, and exceptional U.S. expanded access is a physician-, manufacturer-, IRB-, and FDA-dependent pathway for qualifying serious conditions—not a retail route for an obesity medication that someone simply wants to try.1211


How did The RX Index verify this page?

We built this page from the primary trials, public trial registries, FDA records, sponsor trial pages, and current clinical guidance—keeping every result attached to its population, regimen, timepoint, estimand, and source type. Secondary coverage and public discussion were used to find reader questions and reporting gaps, never to establish a medical or regulatory fact.

Our source order

  1. Peer-reviewed primary trial publications and supplements
  2. FDA databases and FDA policy pages
  3. ClinicalTrials.gov and sponsor trial registries
  4. Peer-reviewed clinical guidance and professional-organization advisories
  5. Sponsor releases, clearly labeled as sponsor-reported
  6. Reputable reporting for business context
  7. Forums and social discussion for language and questions only

The conflict disclosure the trial itself makes

This is material and you shouldn't have to dig it out.

BELIEVE was funded by Eli Lilly. Versanis Bio—a wholly owned Lilly subsidiary—designed and oversaw the trial. A sponsor-employed medical writer assisted with the manuscript. Multiple authors disclosed Lilly or Versanis employment, stock ownership, consulting relationships, patents, or equity interests.1

That does not erase the data. The study was randomized, the methods and limitations were published, and the conflict disclosures are visible. It does mean the sponsor's role belongs next to the result, not hidden beneath it.

What we did not do

We did not use bimagrumab. We did not analyze participant-level data. We did not predict an approval date. We did not turn a research reagent into a dosing tool. We did not invent a medical reviewer, a customer review, or a testimonial. And we did not rank bimagrumab against approved medications as though it were an available option, because it isn't one.

What makes this page original

The RX Index assembled four pieces that do not appear together in the primary paper or any one registry:

  • A normalized 2021-versus-BELIEVE trial table that keeps population, timepoint, and estimand separate
  • A claim-by-claim “what it supports / what it does not support” ledger
  • A live five-record bimagrumab development tracker with a plain-language interpretation column
  • A launch-readiness matrix separating completed evidence from the missing Phase 3, submission, label, formulation, and pricing milestones

The public tables should remain crawlable HTML. Publish the normalized evidence ledger as a versioned CSV as well, using the methodology and fields in the production appendix.

Corrections: report a possible error. We date material verification and log material changes.


Bimagrumab weight loss drug FAQ

Is bimagrumab a GLP-1?

No. Bimagrumab is an investigational monoclonal antibody that blocks activin type II receptor signaling. Semaglutide is a GLP-1 receptor agonist, and tirzepatide acts at GIP and GLP-1 receptors. BELIEVE studied bimagrumab and semaglutide separately and together because they work through different pathways.

Is bimagrumab FDA-approved?

No. As of August 4, 2026, no FDA-approved bimagrumab product exists for weight loss or any other use. It remains in clinical development.10

Can a doctor prescribe bimagrumab?

Not as a routine prescription. No approved product, labeled dose, pharmacy supply, or commercial program exists. Clinical-trial participation is the identifiable public access path for eligible participants.

Is expanded access possible?

U.S. expanded access can sometimes be requested for an investigational drug when a patient has a serious or immediately life-threatening disease or condition, lacks comparable alternatives, and a physician, manufacturer, IRB, and FDA all agree. That is not guaranteed, and we identified no public bimagrumab expanded-access program for obesity.11

Can you buy bimagrumab online?

There is no approved patient product to buy. Scientific suppliers list research-use antibody reagents in laboratory quantities, but those listings do not establish clinical identity, sterility, approved manufacturing, lawful human use, or interchangeability with Lilly's investigational product.18

Can a pharmacy compound bimagrumab?

Not under the ordinary U.S. drug-compounding exemptions. FDA says biological products are not eligible for sections 503A or 503B, and there is no FDA-approved bimagrumab biologic to use as a commercial patient product.17

How much weight did people lose on bimagrumab?

In BELIEVE's post-hoc week-72 efficacy analysis, modeled mean weight change was −10.8% with high-dose bimagrumab, −15.7% with semaglutide 2.4 mg, and −22.1% with the high-dose combination. Those are Phase 2 group estimates, not guaranteed individual outcomes.1

Did bimagrumab build muscle?

High-dose bimagrumab increased DXA-measured lean mass by 2.5% at week 72 in BELIEVE's efficacy analysis. DXA lean mass includes more than skeletal muscle, and the trial did not establish a broad objective improvement in strength or physical function.1

Did bimagrumab prevent lean-mass loss with semaglutide?

It reduced the modeled loss substantially but did not eliminate it. Week-72 DXA lean mass fell 2.9% in the high-dose combination group versus 7.4% with semaglutide 2.4 mg alone—about 61% less relative loss based on those group estimates.1

What does “Musclezempic” mean?

It is a media and internet nickname, not an approved brand name or a precise drug-class description. Bimagrumab is not semaglutide and is not itself a GLP-1 medication.

Is bimagrumab a myostatin inhibitor?

That phrase is common shorthand. The more precise description is an antibody that blocks activin type II receptors, affecting signaling from myostatin, activins, GDF11, and related ligands. It is broader than a molecule that neutralizes myostatin alone.

How was bimagrumab given in BELIEVE?

BELIEVE used 30-minute IV infusions at clinical sites, dosed by body weight. Participants received loading infusions at weeks 1 and 4 and later infusions every 12 weeks. Subcutaneous formulations are being studied, but no commercial route or schedule exists.1813

What are bimagrumab's side effects?

Common bimagrumab-associated adverse events in BELIEVE included muscle spasms or cramps, diarrhea, and acne. Across bimagrumab-only groups, 14.0% to 21.4% stopped treatment because of adverse events, versus 3.6% on placebo.1

Was pancreatitis reported?

Yes. Three serious pancreatitis events occurred during BELIEVE's 48-week primary period—one each in the placebo, bimagrumab 10 mg/kg, and semaglutide 1.0 mg groups. The investigators described the events as infrequent and balanced across groups.1

Did Lilly stop developing bimagrumab?

No. Lilly withdrew one planned Phase 2 study in people with obesity and type 2 diabetes before enrollment for stated strategic business reasons. A separate study in adults without diabetes completed enrollment, and other public research continued.814

Is bimagrumab better than semaglutide?

That is not established. Bimagrumab alone produced less total weight loss than semaglutide 2.4 mg in BELIEVE's week-72 efficacy analysis, while producing a more favorable DXA lean-mass result. Its potential role looks more like a complement to an incretin than a proven replacement.

Is bimagrumab being tested with tirzepatide?

Yes. Lilly's NCT06643728 and the separate Mass General NCT05933499 study evaluate bimagrumab with tirzepatide. No result should be assumed until data are posted or published.812

Is there a Phase 3 bimagrumab obesity trial?

No public Phase 3 bimagrumab obesity trial was found in ClinicalTrials.gov or Lilly's public program at verification on August 4, 2026. That is a current-status claim and should be rechecked monthly.2

When will bimagrumab be available?

No approval or launch date has been announced. January 2027 is a listed trial date for one Phase 2 study, not an approval date. Any precise commercial year is a forecast.

How much will bimagrumab cost?

No verified commercial price exists because there is no approved product, commercial dose, coverage policy, or manufacturer launch program.

Can I join a bimagrumab trial?

Possibly, depending on current recruitment, location, and eligibility. NCT06643728 had completed enrollment, while NCT05933499 was recruiting at verification. Check the official registry and contact the study team; The RX Index cannot determine whether you qualify.812

Is bimagrumab safe?

Phase 2 provides meaningful safety information, not a final answer. BELIEVE reported common adverse events, treatment discontinuations, serious adverse events, laboratory changes, skin cancers, and no deaths. Larger and longer studies are needed to define the benefit-risk profile of any eventual formulation and dose.1


Bottom line: is bimagrumab a real weight loss drug?

Bimagrumab is a real investigational drug with genuine peer-reviewed human results, including 22.1% modeled average weight loss when high-dose bimagrumab was combined with semaglutide in a post-hoc Phase 2 efficacy analysis. It also produced a DXA lean-mass pattern that stood apart inside the same randomized trial. It is unapproved, unavailable as a commercial prescription, and still missing the later-stage evidence needed to turn that signal into a treatment.

Three things to take with you:

It's promising. The fat-mass, estimated visceral-fat, and lean-mass results deserve the attention they're getting. This isn't a molecule with nothing behind it.

It's not settled. The week-72 headline numbers were post hoc with no multiplicity adjustment. As many as one in five people in a bimagrumab-only arm stopped because of adverse events. Strength and broad physical function did not clearly improve. Total hip bone density still declined in several active groups. And the apparent incremental-weight effect changes materially with the estimand.

It's not available. No approval. No patient price. No public Phase 3 obesity trial at verification. No launch date. If you're delaying treatment solely because you expect bimagrumab soon, you're planning around a fact that does not exist.

The most useful thing we can tell you isn't about bimagrumab at all. BELIEVE's high-dose comparison used an FDA-approved semaglutide dose. Everything bimagrumab might one day add, it added on top of an incretin treatment path that already exists.

We'll update this page when the registry, publications, or regulatory status changes. That's a commitment, and it's dated.

### Still not sure which GLP-1 program is right for you? Take our free matching quiz—about 2 minutes → The RX Index's Find My GLP-1 Path tool matches you to treatment paths based on your state, insurance, preferred format, and budget—with source-verified pricing. Independent guidance for choosing your GLP-1 path.


Related guides



Medical disclaimer

This page is for informational and educational purposes only and is not medical advice. Bimagrumab is an investigational drug that is not FDA-approved and is not available as a routine prescription. The trial-scale arithmetic is not a dosing guide. Do not buy or self-administer a research-use antibody reagent. Nothing here should be used to start, stop, delay, or change treatment. Talk with a licensed clinician about your own health, medications, nutrition, symptoms, and treatment options.

Sources

  1. Heymsfield SB, Aronne LJ, Montgomery P, et al. Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial. Nature Medicine. 2026;32:869–882. doi:10.1038/s41591-026-04204-0. NCT05616013.
  2. Heymsfield SB, Coleman LA, Miller R, et al. Effect of bimagrumab vs placebo on body fat mass among adults with type 2 diabetes and obesity: a phase 2 randomized clinical trial. JAMA Network Open. 2021;4(1):e2033457.
  3. Deaton AM, et al. Rare loss-of-function variants in the hepatokine gene INHBE protect from abdominal obesity. Nature Communications. 2022;13:4319.
  4. Akbari P, et al. Multiancestry exome sequencing reveals INHBE mutations associated with favorable fat distribution and protection from diabetes. Nature Communications. 2022;13:4844.
  5. Aditum Bio, Versanis Bio Announces $70 Million Series A Financing, 2021.
  6. Eli Lilly and Company, Lilly to Acquire Versanis to Improve Patient Outcomes in Cardiometabolic Diseases, July 14, 2023. Transaction value stated as up to $1.925 billion.
  7. ClinicalTrials.gov, NCT06643728, and Eli Lilly's public trial page, A Study to Investigate Weight Management With Bimagrumab and Tirzepatide. Status and dates verified August 4, 2026.
  8. Amato AA, et al. Efficacy and safety of intravenous bimagrumab in inclusion body myositis. Neurology. 2021;96(3):e374–e386. The randomized RESILIENT study did not meet its primary endpoint.
  9. U.S. Food and Drug Administration, Drugs@FDA search and bimagrumab orphan-designation record. No bimagrumab approval identified at verification on August 4, 2026.
  10. U.S. Food and Drug Administration, Expanded Access: Information for Patients. Access requirements checked August 4, 2026.
  11. ClinicalTrials.gov, NCT05933499, Effect of Tirzepatide and Bimagrumab on Body Composition, Insulin Sensitivity, and Bone. Status verified August 4, 2026.
  12. ClinicalTrials.gov, NCT06890611, bimagrumab relative-bioavailability and formulation study. Status verified August 4, 2026.
  13. ClinicalTrials.gov, NCT06901349, withdrawn bimagrumab–tirzepatide study in obesity or overweight with type 2 diabetes. Status verified August 4, 2026.
  14. Ro, GLP-1 Insurance Coverage Checker. The live checker listed Ozempic pen, Wegovy pen, and Zepbound pen at verification on August 4, 2026.
  15. Ro, Ro Body Program. Membership pricing verified August 4, 2026: $39 first month; $149 month to month; as low as $74/month with a 12-month plan paid upfront. Medication cost is separate.
  16. U.S. Food and Drug Administration, Compounding and the FDA: Questions and Answers, section addressing biological products and sections 503A/503B. Checked August 4, 2026.
  17. Representative exact-product scientific-supplier listing: GLPBio, Bimagrumab (Anti-ACVR2B Reference Antibody; BYM338), offered in 1 mg and 5 mg packages and labeled “Products are for research use only. Not for human use. We do not sell to patients.” Package sizes and availability can change; checked August 4, 2026.
  18. Regeneron Pharmaceuticals, Phase 2 COURAGE results, September 17, 2025. Twenty-six-week figures and safety statements are sponsor-reported.
  19. Attie KM, et al. Apitegromab for preservation of lean mass during tirzepatide-induced weight loss: a randomized phase 2 trial. Nature Medicine. 2026. EMBRAZE, NCT06445075.
  20. Veru Inc., Full enrollment for the Phase 2b PLATEAU trial, July 27, 2026. Enrollment, design, and projected readout timing are company-reported.
  21. Biohaven Ltd., First-quarter 2026 business update, May 4, 2026. Phase 2 obesity enrollment and expected timing are company-reported.
  22. The Obesity Society, American College of Lifestyle Medicine, American Society for Nutrition, and Obesity Medicine Association, Nutritional priorities to support GLP-1 therapy for obesity, joint clinical advisory.

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