Regeneron weight-loss drug halves muscle loss when combined with semaglutide

Sep 30, 2026

Clinical trial data presented on October 1, 2026, shows that Regeneron's experimental drug trevogrumab, when combined with Novo Nordisk's semaglutide, reduces muscle mass loss by 50% compared to semaglutide alone. This anti-myostatin therapy addresses a major concern of GLP-1 weight-loss drugs. Meanwhile, real-world data shows patients switching to Novo Nordisk's daily Wegovy pill continue to lose weight, highlighting the evolving landscape of obesity treatments.

Trevogrumab muscle preservation results

▪In Regeneron's trial of trevogrumab in nearly 1,000 patients, those taking Novo Nordisk's semaglutide alone lost 6.7% of lean muscle mass over 26 weeks, while those adding 75 milligrams of trevogrumab lost 3.3%, reducing loss by 50%
▪In Regeneron's clinical trial of trevogrumab, patients taking semaglutide combined with a 25-milligram dose of trevogrumab lost 4.7% of their muscle mass over 26 weeks
▪MRI scans of thigh muscle in Regeneron's trial showed that adding a 75-milligram dose of trevogrumab preserved over 70% of muscle mass loss compared to semaglutide alone at 52 weeks

Targeting vulnerable patients

▪Regeneron executive Boaz Hirshberg stated that the greatest potential benefit of trevogrumab could be for patients who begin treatment with lower muscle mass
▪Regeneron selected the 75-milligram once-weekly dose of trevogrumab for future studies and plans to initiate another mid-stage trial in patients over 65 years old

Safety and side effects

▪Trevogrumab administered alone demonstrated a safety profile similar to semaglutide, with no unexpected side effects reported during Regeneron's clinical trial of trevogrumab
▪The combination of trevogrumab and garetosmab preserved more lean mass than trevogrumab alone but caused a high rate of adverse side effects, including muscle spasms

Safety issues with combination treatments

▪During the first 26 weeks of Regeneron's trial of trevogrumab, two participants receiving higher doses of trevogrumab combined with another experimental antibody, garetosmab, died from cardiovascular-related causes
▪Regeneron announced it will not proceed with the triple combination of trevogrumab, garetosmab, and semaglutide due to adverse side effects, including muscle spasms and safety concerns

Interest in anti-myostatins

▪Trevogrumab belongs to a class of medicines that inhibits the protein myostatin, which is biologically linked to the loss of muscle mass
▪Wall Street and the medical community are looking for evidence that next-generation drugs like anti-myostatins can prevent the body from breaking down muscle during weight loss

Concerns over GLP-1 muscle loss

▪The rapid weight loss associated with popular GLP-1 drugs, such as Novo Nordisk's semaglutide, has raised medical concerns regarding the significant loss of accompanying muscle mass
▪Regeneron executive Boaz Hirshberg stated that patients taking GLP-1 receptor agonists typically lose approximately 30% of their weight in the form of lean muscle mass

Wegovy pill study and rollout

▪A 194-patient real-world study showed patients switching from weight-loss injections such as Wegovy and Eli Lilly's Zepbound to Novo Nordisk's daily Wegovy pill lost an average of 4.1% of body weight over three months
▪Novo Nordisk's daily Wegovy pill has been launched in the United States, Britain, Germany, and the United Arab Emirates, with further international rollouts planned
▪In the 194-patient real-world study of Novo Nordisk's Wegovy pill, the proportion of clinically obese participants fell from 87.1% to 65.5% after three months of treatment

Obesity market projections

▪Financial analysts forecast that muscle-preserving therapies such as trevogrumab, with at least a dozen companies currently developing them, could reach $30 billion in annual sales by 2035
▪Novo Nordisk CEO Mike Doustdar stated that weight-loss pills could capture up to half of the global obesity-drug market, which analysts estimate could exceed $100 billion annually by the end of the decade

Debatable claims

▪The trial deaths in Regeneron's study justify greater regulatory caution toward muscle-preserving drugs
▪The risk of muscle loss makes GLP-1 drugs too dangerous for older adults
▪The muscle loss caused by GLP-1 drugs justifies prescribing additional corrective therapies
▪Obesity treatments should prioritize the quality of weight loss over rapid weight reduction