Trevogrumab
Medium EvidenceTrevogrumab (REGN1033) is an investigational fully human anti-myostatin (anti-GDF8) monoclonal antibody from Regeneron being tested as a lean-mass-sparing add-on to semaglutide in the Phase 2 COURAGE obesity trial; adding it to semaglutide prevented roughly half of the ~33% of GLP-1-induced weight loss that normally comes from muscle, and the semaglutide + trevogrumab + garetosmab triplet reached 13.4% weight loss at 26 weeks with only ~7.4% of that loss from lean mass.
What It Is
Trevogrumab (REGN1033) is an investigational fully human monoclonal antibody that binds and neutralizes myostatin (growth differentiation factor 8, GDF-8), a circulating protein that acts as a brake on skeletal-muscle growth. By blocking myostatin, trevogrumab aims to preserve or increase lean muscle mass. Regeneron originally advanced the antibody for age-related sarcopenia, but its most prominent current use is as a muscle-preserving partner for GLP-1 obesity drugs. A recognized limitation of highly effective incretin weight-loss therapy is that a substantial share of the weight lost is lean (muscle) mass rather than fat - roughly a third of semaglutide-induced weight loss in the COURAGE program came from lean tissue. Losing muscle alongside fat is a concern for long-term metabolic health, physical function, and healthy aging, and it has spurred a wave of muscle-directed add-ons including the myostatin-precursor antibody apitegromab, the ActRII-blocking antibody bimagrumab, and the myostatin/activin decoy taldefgrobep alfa. Trevogrumab is Regeneron's entry in this class. The Phase 2 COURAGE trial (NCT06299098) is a large randomized, double-blind study of ~999 participants evaluating trevogrumab - with or without garetosmab (an anti-activin A antibody) - added to semaglutide for obesity, using two consecutive 26-week periods (weight loss then weight maintenance). Complete 26-week results, presented as a late-breaking oral session at the European Association for the Study of Diabetes (EASD) meeting in September 2025, showed that semaglutide alone reduced lean body mass by ~6.5% from baseline, versus ~3.3% with semaglutide + trevogrumab 200 mg and ~3.8% with trevogrumab 400 mg - roughly halving the lean-mass loss. The semaglutide + trevogrumab + garetosmab triplet produced the greatest total weight loss (~13.4%) while limiting the share of weight lost as lean mass to about 7.4%, and adding garetosmab enhanced fat-mass reduction by ~27.3% versus semaglutide alone while preserving over 80% of lean body mass. Tolerability tracked with the added biology: adverse-event discontinuations were 4.6% for semaglutide alone, 4.7% for semaglutide + trevogrumab 200 mg, and 10.6% for trevogrumab 400 mg, with the activin-A-blocking garetosmab arms carrying a higher burden of side effects. The COURAGE trial is expected to complete in late 2026. Trevogrumab is investigational and not approved for any indication.
Regulatory Status
Trevogrumab is in Phase 2 development for muscle preservation during GLP-1-induced weight loss (COURAGE trial, NCT06299098), combined with semaglutide and, in some arms, garetosmab. Complete 26-week results were presented at EASD in September 2025. Not approved for any indication.
Effective: September 2025
View FDA SourceWhy Researchers Study It
Trevogrumab is central to one of the most active questions in obesity medicine: how to keep GLP-1 weight loss from stripping away muscle. Because roughly a third of semaglutide-induced weight loss came from lean mass in COURAGE, a myostatin-blocking antibody that halves that muscle loss - and, in triplet form with an anti-activin-A antibody, preserves more than 80% of lean mass while deepening fat loss - could meaningfully improve the quality of weight loss, physical function, and long-term metabolic outcomes. It also lets researchers dissect the distinct contributions of the myostatin (GDF-8) and activin A pathways to muscle wasting.
Proposed Mechanisms
- Binds and neutralizes circulating myostatin (GDF-8), releasing its inhibitory brake on skeletal-muscle growth to preserve or increase lean mass
- Counteracts the lean-mass loss that accompanies GLP-1-receptor-agonist (semaglutide) weight loss, shifting the composition of weight lost toward fat
- In combination with garetosmab (anti-activin A), blocks a second muscle-atrophy signaling pathway, further preserving lean mass and enhancing fat-mass loss
- Muscle-directed mechanism complements the appetite- and glucose-regulating action of incretin drugs rather than adding to their GI effects
Evidence Snapshot
| Study Type | Model | Outcome | Link |
|---|---|---|---|
| Phase 2 (COURAGE, NCT06299098) - randomized, double-blind, placebo/active-controlled | ~999 adults; parts B/C in obesity - semaglutide +/- trevogrumab (200 or 400 mg) +/- garetosmab; two 26-week periods (weight loss, then maintenance) | Lean body mass fell ~6.5% with semaglutide alone vs ~3.3% (trevogrumab 200 mg) and ~3.8% (400 mg) added - roughly halving lean-mass loss; ~33% of semaglutide weight loss was lean mass, and trevogrumab prevented about half of it | Source |
| Phase 2 (COURAGE) - triplet arm, 26-week analysis | Semaglutide + trevogrumab + garetosmab (anti-activin A) vs semaglutide alone | Triplet reached ~13.4% total weight loss with only ~7.4% of loss from lean mass; garetosmab addition enhanced fat-mass reduction ~27.3% over semaglutide alone while preserving >80% of lean body mass | Source |
| Phase 2 (COURAGE) - safety/tolerability, 26 weeks | Discontinuations due to adverse events across arms | AE-related discontinuation 4.6% (semaglutide alone), 4.7% (semaglutide + trevogrumab 200 mg), 10.6% (trevogrumab 400 mg); garetosmab-containing arms carried a higher side-effect burden | Source |
Commonly Discussed Benefits
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Safety & Cautions
- Investigational - not approved for any indication; Phase 2 COURAGE trial ongoing, expected to complete late 2026
- Data are 26-week results presented at a conference (EASD 2025); full peer-reviewed publication and longer-term outcomes not yet available
- Higher trevogrumab dose (400 mg) and garetosmab-containing (anti-activin A) arms showed greater adverse-event and discontinuation burden
- Long-term effects of chronic myostatin blockade on muscle strength, function, tendons, and safety are not established
- Cross-trial comparisons with other muscle-preserving agents (apitegromab, bimagrumab, taldefgrobep alfa) have significant limitations due to differing designs, GLP-1 partners, and endpoints
Comparisons
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Citations
- [1] Results from Phase 2 COURAGE Trial Demonstrating Potential to Improve Quality of GLP-1 Receptor Agonist-induced Weight Loss by Preserving Lean Mass, Presented at EASD - Regeneron (September 2025) PubMed
- [2] Regeneron Phase 2b Study Shows Antibodies Help Preserve Lean Mass During Weight Loss with Semaglutide - Patient Care Online (2025) PubMed
- [3] Myostatin Blocker Preserves Muscle With GLP-1 Treatment - Medscape (2025) PubMed
- [4] Regeneron's Semaglutide Plus Trevogrumab Combo Demonstrates Superior Fat Loss with Reduced Muscle Wasting in Obesity Trial - Pharmaceutical Executive (2025) PubMed
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