Bimagrumab + Semaglutide Achieves 17.8 kg Weight Loss While Preserving Muscle in Phase 2 Trial | Research

The takeaway

Bimagrumab 30 mg/kg + semaglutide 2.4 mg achieved -17.8 kg weight loss at 48 weeks vs -3.3 kg placebo, with bimagrumab uniquely targeting fat while preserving or increasing lean mass.

-17.8 kg combination
Adding bimagrumab to semaglutide enhanced weight loss beyond either drug alone while targeting fat loss and preserving muscle

What the researchers found

Week 48 weight loss: bimagrumab 30 -9.3 kg; semaglutide 2.4 -14.2 kg; combination -17.8 kg; placebo -3.3 kg (all p<0.001 vs placebo). Improvements continued through week 72. Safety consistent with known profiles.

Why it matters

The combination addresses GLP-1 therapy's biggest weakness (muscle loss) while enhancing weight loss — potentially the most comprehensive obesity treatment to date.

How the study worked

Double-blind, placebo-controlled phase 2 trial (NCT05616013), 507 adults with obesity randomized 1:1:1:1:1:1:1:1:1 to 9 groups, 48-week treatment + 72-week open-label extension.

What this study cannot tell us

Phase 2 trial. Lean mass data not detailed in abstract. Nine-arm design means small groups. Long-term effects beyond 72 weeks unknown.

How to read the evidence

Phase 2 RCT with multiple treatment arms. Strong efficacy signal with consistent safety. Phase 3 confirmation needed.

When this study was published

Published in 2025, NCT05616013.

The bigger picture

Combining anabolic (muscle-building) with catabolic (fat-burning) therapies represents a new paradigm in obesity treatment: lose fat while keeping or building muscle.

Questions still open

How much lean mass was preserved vs semaglutide alone?
Would the combination be cost-effective given two expensive drugs?
Should bimagrumab be added to all GLP-1 therapy for muscle preservation?

Common questions

What is bimagrumab?

An antibody that blocks activin receptors to prevent muscle breakdown and promote lean mass growth. Combined with semaglutide, it targets fat loss while keeping muscle — addressing the main concern with GLP-1 weight loss drugs.

Is this better than semaglutide alone?

The combination lost 17.8 kg vs 14.2 kg for semaglutide alone and 3.3 kg for placebo. The key advantage is muscle preservation — bimagrumab protects lean mass while semaglutide burns fat.

Read the original research

Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial.

Nature medicine

View on PubMed ↗Publisher’s paper ↗

Citation

Heymsfield, Steven B; Aronne, Louis J; Montgomery, Penelope; Klickstein, Lloyd B; Coleman, Laura A; Dole, Kiran; Mindeholm, Linda; Spruill, Susan; Li, Xingyuan; Attie, Kenneth M. (2026). Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial.. Nature medicine. https://doi.org/10.1038/s41591-026-04204-0