Bimagrumab
updated
In a randomized obesity trial, bimagrumab reduced weight and fat mass while increasing lean mass. The antibody remains investigational, and the trial did not establish better strength or mobility.
Monoclonal antibody against activin type II receptors A and B
- Investigational monoclonal antibody
- BELIEVE tested intravenous dosing every 12 weeks
- Blocks activin type II receptors A and B
Is bimagrumab approved for obesity?
FDA Drugs@FDA and Purple Book records contained no exact-name bimagrumab approval. BELIEVE was a phase 2 trial, so its results support development rather than prescribing an approved obesity product.
Bimagrumab has also been studied in muscle-wasting settings with different populations and outcomes. It remains unapproved for obesity.
FDA records · bimagrumab status
Regulatory database record set
FDA Drugs@FDA and Purple Book records
The cited FDA databases contain no exact-name U.S. approval record for bimagrumab.
- Participants / model
- United States drug and biologic approvals
- Treatment
- Bimagrumab
- Study design
- Exact-name U.S. approval coverage
What did BELIEVE show for bimagrumab, semaglutide, and their combination?
At week 48, least-squares mean absolute weight change was -9.3 kg with intravenous bimagrumab 30 mg/kg every 12 weeks, -14.2 kg with semaglutide 2.4 mg weekly, -17.8 kg with the high-dose combination, and -3.3 kg with placebo. All active comparisons were significant versus placebo.
The 507-person trial randomized participants across nine arms. Comparisons to semaglutide shown in the paper were not multiplicity adjusted, so they do not establish a definitive rank ordering among the arms.
Common bimagrumab adverse events included muscle spasms, diarrhea, and acne.
| Arm | Mean change |
|---|---|
| Bimagrumab 30 mg/kg IV | -9.3 kg |
| Semaglutide 2.4 mg SC | -14.2 kg |
| High-dose combination | -17.8 kg |
| Placebo | -3.3 kg |
BELIEVE · randomized phase 2 results
Randomized trial
Heymsfield et al., Nature Medicine, 2026
In 507 adults, active regimens reduced weight more than placebo at week 48; the full report provides arm-level adverse-event, serious-event, and discontinuation data and says post-treatment follow-up is ongoing.
- Participants / model
- Adults with obesity or overweight plus a complication, without diabetes
- Treatment
- Bimagrumab IV every 12 weeks, semaglutide SC weekly, combinations, or placebo
- Follow-up
- 48 weeks, followed by extension and withdrawal follow-up
- Study design
- Randomized phase 2 trial with blinded bimagrumab and open-label semaglutide
- Funding
- Eli Lilly
The paper's active-comparator P values were not adjusted for multiplicity.
Read the original sourceWhat did BELIEVE report about safety and stopping treatment?
Through week 48, treatment-emergent adverse events occurred in 91.1% to 98.2% of active-treatment groups versus 74.5% with placebo. Serious adverse events occurred in 8.8% to 12.5% with bimagrumab alone, 1.8% to 10.7% with semaglutide alone, 3.6% to 9.1% with combinations, and 3.6% with placebo; no deaths occurred.
Adverse-event discontinuation ranged from 14.0% to 21.4% with bimagrumab alone, 3.6% to 8.8% with semaglutide alone, 5.3% to 12.5% with combinations, and was 3.6% with placebo. Five participants stopped bimagrumab monotherapy because of muscle spasms; six participants stopped combination therapy because of nausea.
BELIEVE · randomized phase 2 results
Randomized trial
Heymsfield et al., Nature Medicine, 2026
In 507 adults, active regimens reduced weight more than placebo at week 48; the full report provides arm-level adverse-event, serious-event, and discontinuation data and says post-treatment follow-up is ongoing.
- Participants / model
- Adults with obesity or overweight plus a complication, without diabetes
- Treatment
- Bimagrumab IV every 12 weeks, semaglutide SC weekly, combinations, or placebo
- Follow-up
- 48 weeks, followed by extension and withdrawal follow-up
- Study design
- Randomized phase 2 trial with blinded bimagrumab and open-label semaglutide
- Funding
- Eli Lilly
The paper's active-comparator P values were not adjusted for multiplicity.
Read the original sourceDid lean-mass gains translate to better strength or mobility?
In a separate hip-fracture trial, bimagrumab increased lean mass but did not significantly improve gait speed or the short physical performance battery. Weight and imaging changes alone do not establish better strength or mobility.
In older adults recovering from hip fracture, the imaging change did not translate into better gait speed or short physical performance battery scores.
Hip fracture study · mass versus function
Randomized trial
Rooks et al., Journal of Cachexia, Sarcopenia and Muscle, 2022
Bimagrumab increased lean body mass but did not significantly improve gait speed or short physical performance battery outcomes.
- Participants / model
- Older adults after hip-fracture surgery
- Treatment
- Intravenous bimagrumab or placebo
- Follow-up
- 24 weeks
- Study design
- Randomized, double-blind, placebo-controlled trial
This recovery population differs from adults enrolled for obesity treatment.
Read the original sourceWhat did the earlier obesity and diabetes trial show?
The 2021 randomized trial reported favorable fat-mass and lean-mass changes. Its principal analysis used 58 completers and 80% confidence intervals, and the paper later received two corrections.
The paper reported 80% confidence intervals rather than the more common 95% intervals. Its principal analysis included only the 58 participants who completed the trial.
Early bimagrumab trial · corrected analysis
Randomized trial with corrections
Heymsfield et al., JAMA Network Open, 2021
The trial reported loss of fat mass and gain of lean mass, using a 58-completer analysis and 80% confidence intervals; correction notices followed.
- Participants / model
- Adults with obesity and type 2 diabetes
- Treatment
- Intravenous bimagrumab or placebo
- Follow-up
- 48 weeks
- Study design
- Randomized, double-blind, placebo-controlled phase 2 trial
The principal efficacy analysis included 58 completers and reported 80% confidence intervals; two correction notices followed.
Read the original sourceDoes intravenous BELIEVE evidence establish a subcutaneous product?
No. BELIEVE tested intravenous bimagrumab at weight-based doses every 12 weeks. Separate pharmacokinetic work can inform subcutaneous development, but clinical efficacy and safety cannot be assumed identical across formulation and route.
The trial included withdrawal follow-up after week 72, but that follow-up was still ongoing when the report was published. Antibody half-life alone cannot show that weight or body-composition changes persist.
BELIEVE · randomized phase 2 results
Randomized trial
Heymsfield et al., Nature Medicine, 2026
In 507 adults, active regimens reduced weight more than placebo at week 48; the full report provides arm-level adverse-event, serious-event, and discontinuation data and says post-treatment follow-up is ongoing.
- Participants / model
- Adults with obesity or overweight plus a complication, without diabetes
- Treatment
- Bimagrumab IV every 12 weeks, semaglutide SC weekly, combinations, or placebo
- Follow-up
- 48 weeks, followed by extension and withdrawal follow-up
- Study design
- Randomized phase 2 trial with blinded bimagrumab and open-label semaglutide
- Funding
- Eli Lilly
The paper's active-comparator P values were not adjusted for multiplicity.
Read the original sourceBimagrumab SC · route study
Early-phase trial
Garito et al., Clinical Pharmacokinetics, 2023
Early human studies characterized subcutaneous exposure and pharmacodynamic markers.
- Participants / model
- Healthy participants and study populations in early-phase cohorts
- Treatment
- Subcutaneous bimagrumab dose cohorts
- Follow-up
- Single and repeat-dose follow-up
- Study design
- Early-phase pharmacokinetic study
Exposure data do not establish obesity efficacy for the subcutaneous route.
Read the original sourceDoes BELIEVE show that weight or body-composition changes persist after withdrawal?
The BELIEVE report covers assigned treatment through week 72 and says post-treatment follow-up was ongoing. It contains no completed randomized withdrawal result showing that weight or body-composition changes persist after treatment stops.
A long antibody half-life can prolong exposure. It cannot by itself establish lasting fat loss, lean-mass preservation, strength, or clinical benefit after withdrawal.
BELIEVE · randomized phase 2 results
Randomized trial
Heymsfield et al., Nature Medicine, 2026
In 507 adults, active regimens reduced weight more than placebo at week 48; the full report provides arm-level adverse-event, serious-event, and discontinuation data and says post-treatment follow-up is ongoing.
- Participants / model
- Adults with obesity or overweight plus a complication, without diabetes
- Treatment
- Bimagrumab IV every 12 weeks, semaglutide SC weekly, combinations, or placebo
- Follow-up
- 48 weeks, followed by extension and withdrawal follow-up
- Study design
- Randomized phase 2 trial with blinded bimagrumab and open-label semaglutide
- Funding
- Eli Lilly
The paper's active-comparator P values were not adjusted for multiplicity.
Read the original sourceBimagrumab SC · route study
Early-phase trial
Garito et al., Clinical Pharmacokinetics, 2023
Early human studies characterized subcutaneous exposure and pharmacodynamic markers.
- Participants / model
- Healthy participants and study populations in early-phase cohorts
- Treatment
- Subcutaneous bimagrumab dose cohorts
- Follow-up
- Single and repeat-dose follow-up
- Study design
- Early-phase pharmacokinetic study
Exposure data do not establish obesity efficacy for the subcutaneous route.
Read the original sourceStudies and sources
FDA records · bimagrumab status
Regulatory database record set
FDA Drugs@FDA and Purple Book records
The cited FDA databases contain no exact-name U.S. approval record for bimagrumab.
- Participants / model
- United States drug and biologic approvals
- Treatment
- Bimagrumab
- Study design
- Exact-name U.S. approval coverage
BELIEVE · randomized phase 2 results
Randomized trial
Heymsfield et al., Nature Medicine, 2026
In 507 adults, active regimens reduced weight more than placebo at week 48; the full report provides arm-level adverse-event, serious-event, and discontinuation data and says post-treatment follow-up is ongoing.
- Participants / model
- Adults with obesity or overweight plus a complication, without diabetes
- Treatment
- Bimagrumab IV every 12 weeks, semaglutide SC weekly, combinations, or placebo
- Follow-up
- 48 weeks, followed by extension and withdrawal follow-up
- Study design
- Randomized phase 2 trial with blinded bimagrumab and open-label semaglutide
- Funding
- Eli Lilly
The paper's active-comparator P values were not adjusted for multiplicity.
Read the original sourceHip fracture study · mass versus function
Randomized trial
Rooks et al., Journal of Cachexia, Sarcopenia and Muscle, 2022
Bimagrumab increased lean body mass but did not significantly improve gait speed or short physical performance battery outcomes.
- Participants / model
- Older adults after hip-fracture surgery
- Treatment
- Intravenous bimagrumab or placebo
- Follow-up
- 24 weeks
- Study design
- Randomized, double-blind, placebo-controlled trial
This recovery population differs from adults enrolled for obesity treatment.
Read the original sourceEarly bimagrumab trial · corrected analysis
Randomized trial with corrections
Heymsfield et al., JAMA Network Open, 2021
The trial reported loss of fat mass and gain of lean mass, using a 58-completer analysis and 80% confidence intervals; correction notices followed.
- Participants / model
- Adults with obesity and type 2 diabetes
- Treatment
- Intravenous bimagrumab or placebo
- Follow-up
- 48 weeks
- Study design
- Randomized, double-blind, placebo-controlled phase 2 trial
The principal efficacy analysis included 58 completers and reported 80% confidence intervals; two correction notices followed.
Read the original sourceBimagrumab SC · route study
Early-phase trial
Garito et al., Clinical Pharmacokinetics, 2023
Early human studies characterized subcutaneous exposure and pharmacodynamic markers.
- Participants / model
- Healthy participants and study populations in early-phase cohorts
- Treatment
- Subcutaneous bimagrumab dose cohorts
- Follow-up
- Single and repeat-dose follow-up
- Study design
- Early-phase pharmacokinetic study
Exposure data do not establish obesity efficacy for the subcutaneous route.
Read the original sourceWhy is Bimagrumab in A tier?
A reflects randomized body-composition data, including the 507-person BELIEVE phase 2 trial. Bimagrumab remains investigational, and its intravenous results do not establish preserved physical function or efficacy for a subcutaneous product.
read Bimagrumab in the reptides guide, chapter 28: 6 pages, free to read.