Bimagrumab

Bimagrumab is an investigational activin type II receptor antibody with randomized intravenous evidence for reducing body weight and fat mass while preserving or increasing lean mass. FDA's July 2026 Purple Book data snapshot had no bimagrumab or listed development-identifier entry when checked on August 15, 2026.

tier A · weight loss · 507 adults in the completed BELIEVE trial

verdict

BELIEVE showed direct 48-week weight and body-composition effects in 507 adults without diabetes. The trial was completed and published, but it does not supply approval, cardiovascular-outcome, mortality, function, or post-treatment durability evidence.

the core tension

The weight and body-composition signal is direct and substantial enough for a Tier A page. The record still stops at the studied interval, population, and intravenous product, with function, hard outcomes, approval, and long-term durability unresolved.

what it is

Bimagrumab, also identified as BYM338 and LY3985863 in development records, is a monoclonal antibody against activin type II receptors A and B. The FDA substance record supplies identity, not approval.

what it does

It binds the ligand-facing surfaces of ActRIIA and ActRIIB and blocks ligand signaling. That receptor mechanism supports the biological rationale but does not itself prove weight loss or safety.

origin

The FDA orphan record concerns sporadic inclusion body myositis and says the product was not approved for that indication. The obesity evidence comes from later investigational trials, chiefly intravenous regimens.

does it work

For the studied weight and body-composition outcomes, yes. BELIEVE reported mean week-48 weight changes of -9.3 kg with IV bimagrumab 30 mg/kg, -14.2 kg with semaglutide 2.4 mg, -17.8 kg with their highest-dose combination, and -3.3 kg with placebo. Those comparisons do not establish a hard clinical outcome or a different route.

key facts

• molecular formula: not supplied as a single small-molecule formula in the FDA SRS record
• molecular weight: not supplied as one exact molecular weight in the FDA SRS record
• amino acids: monoclonal antibody, not represented as a short peptide sequence
• half-life: not stated as a universal value; the cited older-adult study supports target-mediated disposition and about 40% SC bioavailability
• type: monoclonal antibody against activin type II receptors A and B
• CAS: 1356922-05-8
• 507 actual enrollment in completed BELIEVE
• 58 completers in the corrected earlier efficacy analysis
• 68 participants in the cardiac-imaging trial, not an outcomes trial

frequently asked questions

Was BELIEVE still ongoing when its 2026 paper appeared?

No. BELIEVE NCT05616013 was completed with results posted and actual enrollment 507; it is not an ongoing trial.

What corrections apply to the earlier diabetes and obesity trial?

PMID 33439265 has two linked correction notices. Its reported efficacy analysis used 58 completers and 80% confidence intervals, so those details stay beside the corrected numbers.

Was the 68-person older-adult study a cardiovascular-outcomes trial?

No. The 68-person cardiac imaging study used data collected from 2013 to 2015, was published in 2026, and was not a cardiovascular-outcomes trial. It measured MRI and body-composition endpoints. The sponsor funded the study and participated in design and interpretation.

Does improved lean mass prove better function?

No. Body composition and weight did not establish function, cardiovascular events, mortality, or durability. The hip-fracture trial increased lean mass without significant gait-speed or performance-battery improvement.

Is bimagrumab approved for obesity?

No FDA-licensed bimagrumab product was identified in the July 2026 Purple Book data snapshot checked on August 15, 2026. Bimagrumab remains investigational, and an orphan designation is not approval.

related peptides

• semaglutide: The bimagrumab evidence cited on this page does not establish semaglutide's approval, safety framework, or outcomes outside the BELIEVE comparator arms.
• tirzepatide: The bimagrumab evidence cited on this page does not establish tirzepatide's identity, approval, or outcomes, and no result is transferred from a combination program.

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.