Bimagrumab

BELIEVE at 48 weeks

The phase 2 trial randomized 507 adults with obesity across nine groups. In the treatment-regimen analysis, average weight changes were -9.3 kg with high-dose bimagrumab, -14.2 kg with semaglutide 2.4 mg, -17.8 kg with their combination and -3.3 kg with placebo.⁷⁹¹

Read the result with its time point

The low-dose bimagrumab comparison with placebo was not statistically significant. Week-48 comparisons were not adjusted for multiple testing. The 72-week extension used a different analysis, and all of those analyses were post hoc.⁷⁹¹

Current development

Lilly lists bimagrumab in phase 2 for obesity. Trials with tirzepatide are ongoing; no results were posted in the records checked September 30, 2026.^792,793,794

Fat, lean mass and strength

The earlier diabetes trial

Seventy-eight adults were randomized, 75 received treatment and 58 completed the study. At 48 weeks, bimagrumab recipients had reported changes of -7.5 kg in fat mass and +1.7 kg in lean mass. The analysis used 80% confidence intervals.^795,796

Corrections to the record

The corrected placebo HbA1c change was an increase of 0.04 percentage points, compared with a decrease of 0.76 with bimagrumab. A second correction also changed the Matsuda insulin-sensitivity P value to .10. Some archived paper text still carries the earlier values.^795,797,798

The function results

The 251-person RESILIENT study did not meet its main walking endpoint. Larger hip-fracture and sarcopenia trials likewise found mass gains without clear overall gains in walking or physical performance. Small early trials and selected subgroups produced more favorable signals.^{799,800,801,802}

After stopping

BELIEVE’s posted results include efficacy measurements through week 72. Its planned week-104 withdrawal outcome was not found in the registry results checked here, leaving long-term fat-loss maintenance unanswered.^803,791

Side effects and open questions

Cholesterol and bone measurements

At 48 weeks, LDL cholesterol rose by 23.3 mg/dL with high-dose bimagrumab alone, versus a 2.6 mg/dL fall with placebo. Hip bone density declined by 2.2% to 2.3% with high-dose combinations and by 0.8% with placebo.⁷⁹¹

Did the COPD trial report side effects?

Yes. Its registry records serious events in 4 of 33 bimagrumab recipients and 3 of 34 placebo recipients, along with other adverse events in both groups. A later Chinese review incorrectly described this trial as having no adverse events.^804,805

Routes under study

BELIEVE used intravenous bimagrumab. Separate pharmacokinetic studies tested subcutaneous administration; approximately 40% bioavailability was reported in an older-adult study. Product formulation, dose and route belong with each result.^806,791

Common questions

Answers from the studies and current trial records.

01 What happens when bimagrumab is combined with semaglutide?

In BELIEVE, 507 adults with obesity were randomized across nine groups. At 48 weeks, the high-dose combination lost 17.8 kg on average, compared with 14.2 kg for semaglutide 2.4 mg alone and 3.3 kg for placebo, under the treatment-regimen analysis. These comparisons used unadjusted P values.⁷⁹¹

02 Does it preserve muscle, and does that make people stronger?

Bimagrumab increased DXA lean mass when used alone and reduced lean-mass loss when combined with semaglutide. Lean mass includes tissues beyond skeletal muscle. Larger studies in inclusion body myositis, hip-fracture recovery and sarcopenia found gains in mass without clear overall improvements in walking or physical performance.^{791,799,800,801}

03 How much fat did people lose?

Fat mass is one part of body weight. In the earlier diabetes/obesity trial, 75 people received treatment and 58 completed follow-up. At 48 weeks, the reported bimagrumab changes were -7.5 kg of fat, +1.7 kg of lean mass and -5.9 kg of total weight; the study used 80% confidence intervals.^795,797,798

04 Has anyone actually received it in a clinical trial?

Yes. Bimagrumab has been studied in obesity, type 2 diabetes, inclusion body myositis, sarcopenia, COPD and hip-fracture recovery. The largest published obesity study, BELIEVE, randomized 507 adults; 501 received at least one dose of study treatment.^{791,807,800,801,803}

05 What about combining it with tirzepatide?

Human trials are studying that combination. On September 30, 2026, NCT06643728 listed 252 enrolled participants and was active, not recruiting; NCT05933499 was recruiting with an estimated enrollment of 63. Neither registry record included posted results.^793,794

06 Is bimagrumab a peptide, a GLP-1 drug or something else?

Bimagrumab is a monoclonal antibody, a large protein that binds activin type II receptors A and B. Its development names include BYM338 and LY3985863. It blocks receptor signaling involved in muscle and fat regulation; GLP-1 medicines act through a different receptor.^808,790,791

07 Can it be prescribed now, and what will it cost?

Bimagrumab remains investigational. Lilly’s August 5, 2026 pipeline lists it in phase 2 for obesity, and the trial records describe ongoing development. An approved product price and routine prescribing route have not been established by these records.^792,793

08 What doses and routes have researchers studied?

BELIEVE studied intravenous bimagrumab at 10 or 30 mg/kg, with loading doses at weeks 1 and 4 followed by dosing every 12 weeks. Separate studies tested subcutaneous administration; one older-adult pharmacokinetic study estimated approximately 40% subcutaneous bioavailability. These are study regimens for investigational formulations.^791,806

09 What side effects showed up?

Muscle spasms, diarrhea and acne were common in BELIEVE. With high-dose bimagrumab alone, 42 of 57 treated participants reported spasms, compared with 3 of 55 on placebo. Adverse events led 12 of 56 lower-dose and 8 of 57 higher-dose bimagrumab recipients to stop treatment.⁷⁹¹

10 Is it the same as follistatin or other myostatin drugs?

No. Bimagrumab binds activin receptors A and B. Other approaches bind myostatin itself, activin A or several circulating ligands. These targets and products differ, and the cited studies do not establish a clinical ranking across them.^790,791

11 Do the studies show a bodybuilding benefit?

The clinical evidence centers on people with obesity, muscle-wasting conditions or experimentally induced muscle loss. In a 24-person study of young men after leg casting, thigh volume recovered above baseline with bimagrumab while knee-extension strength returned to baseline in both groups. A bodybuilding performance benefit remains unestablished.^809,791

12 Does the fat stay off after treatment stops?

Long-term maintenance after stopping remains an open question. BELIEVE planned follow-up after treatment ended at week 72, but no week-104 withdrawal outcome was identified in its posted registry results.^791,803,810

13 What happened to cholesterol and heart measures?

At 48 weeks in BELIEVE, LDL cholesterol rose by 23.3 mg/dL with high-dose bimagrumab alone, versus a 14.0 mg/dL fall with semaglutide 2.4 mg and a 2.6 mg/dL fall with placebo. A separate 68-person older-adult study assessed cardiac structure and function over months. Cardiovascular-event effects remain unestablished.^791,811

14 What do we know about bones, hormones and pregnancy?

BELIEVE measured hip bone-density declines of 2.1% with semaglutide and 2.2% to 2.3% with high-dose combinations at 48 weeks, versus 0.8% with placebo. An earlier healthy-adult study found reversible suppression of follicle-stimulating hormone in women. Pregnancy and fertility outcomes remain unestablished in these sources.^791,812

15 Is bimagrumab banned in tested sport?

Yes. The 2026 WADA List explicitly names bimagrumab under S4.3 and prohibits it both in and out of competition. The published 2027 List retains that classification.^813,814