Lilly's bimagrumab-semaglutide combo posted 17.8 kg weight loss at week 48
A completed Phase 2 trial found high-dose bimagrumab plus semaglutide 2.4 mg beat either drug alone on weight loss, with results now posted after the study closed in June 2025.
Executive Summary
- A Phase 2 trial testing bimagrumab, an antibody that blocks activin receptor signaling, alongside semaglutide in obesity has posted its primary weight-loss result, showing the combination outperformed either drug given alone.
- Bimagrumab targets a muscle-preserving pathway distinct from GLP-1 receptor agonism, testing whether adding it to an already-established weight-loss drug class can extend the amount of weight lost.
- The activin-blocking approach faces almost no same-target competition in obesity, with only one other bimagrumab trial reaching Phase 2 in a related metabolic indication, while GLP-1-class drugs from Lilly, Novo Nordisk, and others dominate the broader obesity field.
- Serious adverse events ran higher in bimagrumab-containing arms than commonly seen with GLP-1 monotherapy, a tolerability question that will shape whether the combination advances toward later-phase testing.
The readout
The trial, registered as NCT05616013, completed on June 14, 2025, and posted results on ClinicalTrials.gov on July 18, 2025. Its primary endpoint measured change from baseline in body weight at week 48. Bimagrumab at 30 mg/kg reduced body weight by 9.3 kg compared with 3.3 kg for placebo, semaglutide 2.4 mg alone produced a 14.2 kg reduction, and the combination of bimagrumab 30 mg/kg with semaglutide 2.4 mg produced a 17.8 kg reduction, all statistically significant against placebo (p<0.001). NCT05616013+1Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseNCT05616013Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseJul 18, 2025
Probability of SuccessBased on the AppliedXL Probability of Success model. For more information about the methodology, read the research here.
How it was done
The randomized, double-blind, placebo-controlled study enrolled 507 adults with obesity or overweight across the United States, Australia, and New Zealand, assigning them to nine arms combining three bimagrumab doses (0, 10, and 30 mg/kg, intravenous) with three semaglutide doses (none, 1.0 mg, and 2.4 mg, subcutaneous) over a 48-week core treatment period. Body weight change was assessed by mixed-model repeated measures analysis, and secondary measures tracked body composition by DXA and bioelectrical impedance, waist circumference, and patient-reported quality of life through week 72. NCT05616013Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseNCT05616013
Mechanism and stake
Bimagrumab blocks the activin type II receptor (ACVR2B), a target studied for preserving lean muscle mass during weight loss, a different mechanism from the GLP-1 receptor agonism that drives semaglutide and most other approved obesity drugs. The trial tests whether pairing the two mechanisms adds weight loss beyond what GLP-1 agonism alone delivers, and the posted 17.8 kg combination result against semaglutide's 14.2 kg monotherapy result speaks directly to that question. NCT05616013+1Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseNCT05616013Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseJul 18, 2025
Competitive position
The ACVR2B-obesity space carries almost no same-target competition: Novartis's bimagrumab in type 2 diabetes (NCT03005288) is the only other direct comparator, and the broader obesity field of over 300 active trials is dominated by GLP-1 receptor agonists such as Lilly's own tirzepatide and retatrutide and Novo Nordisk's semaglutide and CagriSema, none of which share bimagrumab's target. Given that GLP-1 monotherapy already sets an established weight-loss benchmark in this field, a mechanism add-on has to clear a durability and tolerability bar, not merely add weight loss versus placebo, to matter competitively.
Safety signal
Serious adverse events occurred in 5 to 9 patients per arm across the nine roughly 55-to-57-patient treatment groups, with bimagrumab-containing arms generally showing more serious events than the placebo-plus-semaglutide arms. A related Lilly trial pairing bimagrumab with tirzepatide in adults with type 2 diabetes and obesity, NCT06901349, was withdrawn in June 2025. NCT05616013Safety and Efficacy of Bimagrumab and Semaglutide in Adults Who Are Overweight or ObeseNCT05616013
Track record
Eli Lilly and Company completes 93% of its trials globally across 1,810 recorded studies, a rate that gives no particular reason to doubt this trial's own outcome disclosure. The company still runs one other bimagrumab trial actively, pairing it with tirzepatide in obesity, which remains active and not recruiting.
This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.