Bimagrumab

ID: bimagrumab

Aliases: BYM338, ActRII antibody, activin type II receptor antibody

Type: compound

Route/form: intravenous infusion in clinical trials

Status: investigational

Evidence level: human RCT

Best data tier: human controlled/review; exact-use indirect

Support scope: human, review/regulatory, context

Source types: clinical_trial_registry, human_physiology, human_rct, human_rct_negative, human_trial, meta_analysis, review

Linked sources: 10

Broad outcomes: Fat loss / metabolic health, Muscle growth / performance / recovery, PEDs / AAS / thermogenics

Reading note: These are curation notes anchored to linked sources, not a clinical recommendation or protocol.

Targets / mechanism

• activin type II receptor blockade
• myostatin/activin signaling inhibition
• lean mass gain and fat mass reduction signal

Optimization domains

• metabolic
• obesity
• type 2 diabetes
• body composition
• muscle
• sarcopenia
• myostatin
• activin signaling

Research basis

• Human phase 2 obesity/T2D data and BELIEVE semaglutide-combination data support fat-mass loss, lean-mass preservation/gain, and body-composition effects from ActRII blockade.
• Sarcopenia trials and body-composition meta-analysis are important because they test whether increased lean mass translates into physical function, not just DXA/MRI changes.
• ActRII blockade gives a mechanistic bridge between myostatin/activin negative regulation, muscle mass, adipose biology, and insulin sensitivity.

Limits, risks, and missing evidence

• It is an investigational IV biologic, not a supplement-like or casually deployable body-composition tool.
• In inclusion body myositis and sarcopenia contexts, lean-mass signals do not always translate into robust functional improvement, so lean mass is not automatically useful performance.
• Muscle spasms, GI issues in combinations, trial dropouts, and long-term pathway safety matter for any obesity-adjunct framing.

Risk flags

• investigational
• monoclonal antibody
• IV infusion
• muscle spasms
• diarrhea
• limited long term data
• medical supervision
• cost burden
• lean mass not function

Linked papers, labels, and reviews

1. Effect of Bimagrumab vs Placebo on Body Fat Mass Among Adults With Type 2 Diabetes and Obesity: A Phase 2 Randomized Clinical Trial
   human_rct / pubmed_bimagrumab_obesity_t2d_phase2_2021
   Direct obesity/T2D phase 2 RCT; ActRII blockade reduced fat mass, increased lean mass, and improved metabolic markers over 48 weeks.
2. Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial
   human_rct / pmc_bimagrumab_semaglutide_phase2_2026
   Peer-reviewed BELIEVE phase 2 obesity trial testing IV bimagrumab, SC semaglutide, and combinations; relevant to fat-share of weight loss, lean-mass preservation, muscle-spasm tolerability, and combination-therapy questions.
3. Bimagrumab improves body composition and insulin sensitivity in insulin-resistant individuals
   human_physiology / pubmed_bimagrumab_insulin_resistance_2017
   Small randomized human study using insulin-sensitivity and body-composition endpoints after bimagrumab exposure.
4. Safety and efficacy of intravenous bimagrumab in inclusion body myositis (RESILIENT): a randomised, double-blind, placebo-controlled phase 2b trial
   human_rct_negative / sciencedirect_bimagrumab_resilient_2019
   Large sIBM phase 2b trial; important negative functional-endpoint context despite muscle/lean-mass biology.
5. Efficacy and Safety of Bimagrumab in Sporadic Inclusion Body Myositis: Long-term Extension of RESILIENT
   human_trial / pubmed_bimagrumab_resilient_extension_2021
   Long-term extension of the sIBM program; reports IV dosing, safety, progressive functional decline, and limited durable functional signal.
6. Bimagrumab: an investigational human monoclonal antibody against activin type II receptors for treating obesity
   review / pubmed_bimagrumab_obesity_review_2024
   Recent review summarizing bimagrumab mechanism, obesity/T2D trial evidence, and investigational status.
7. BELIEVE: Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or Obese
   clinical_trial_registry / clinicaltrials_believe_bimagrumab_semaglutide
   ClinicalTrials.gov registry for BELIEVE; confirms 507 enrollment, completed status, IV bimagrumab plus open-label SC semaglutide design, and body-composition rationale.
8. Effect of Bimagrumab on body composition: a systematic review and meta-analysis
   meta_analysis / pubmed_bimagrumab_bodycomp_meta_2024
   Meta-analysis across bimagrumab studies for body composition and physical-performance context; important for separating lean-mass changes from functional benefit.
9. Treatment of Sarcopenia with Bimagrumab: Results from a Phase II, Randomized, Controlled, Proof-of-Concept Study
   human_rct / pubmed_bimagrumab_sarcopenia_poc_2017
   Phase 2 proof-of-concept sarcopenia trial; supports thigh muscle volume/lean-mass signals and helps test whether body-composition effects translate to function.
10. Bimagrumab vs Optimized Standard of Care for Treatment of Sarcopenia in Community-Dwelling Older Adults: A Randomized Clinical Trial
    human_rct / pubmed_bimagrumab_sarcopenia_2020
    Larger sarcopenia RCT with optimized standard care; important functional-outcome counterweight to simple lean-mass enthusiasm.