Weight-Loss Drugs Reduce Muscle More Than Expected

Losing muscle mass is not the same as losing muscle strength and function, clinicians say.

Apr. 20, 2026 at 7:54am

Got story updates? Submit your updates here. ›

A glowing, neon outline of a human muscle group, such as the biceps or quadriceps, against a deep, dark background, conceptually illustrating the impact of weight-loss drugs on muscle mass.Weight-loss drugs may reduce muscle mass more than expected, highlighting the need to monitor physical function alongside weight loss.Chapel Hill Today

A new study presented at the American College of Physicians Internal Medicine (ACP-IM) Meeting in San Francisco found that blockbuster weight-loss drugs cause muscle loss exceeding clinician expectations. While losing fat often leads to some muscle loss, the researchers were surprised by the amount of muscle mass lost. However, the study did not directly link this muscle loss to declines in strength or physical function.

Why it matters

The absence of data on functional outcomes leaves a clinical gap, underscoring the need to assess strength and mobility alongside weight loss in patients receiving these therapies. Muscle mass naturally diminishes with age, so any additional loss is especially significant in older adults and could impact their quality of life.

The details

The systematic review included 36 randomized clinical trials that measured changes in fat and muscle mass among adults who used incretin-based obesity medications like liraglutide, semaglutide, tirzepatide, or dulaglutide. The researchers found that 68% of people who used the drugs exceeded the 25% muscle loss threshold, compared to 50% of people who used lifestyle interventions or placebos. None of the studies measured whether this loss of muscle mass correlated with loss of strength or function.

  • The study was presented at the American College of Physicians Internal Medicine (ACP-IM) Meeting in San Francisco in 2026.

The players

John Batsis

An associate professor of medicine in the Division of Geriatric Medicine at The University of North Carolina at Chapel Hill, who led the study.

Jaime Almandoz

A professor of medicine and medical director of the Weight Wellness Program at UT Southwestern Medical Center in Dallas, who was not involved in the study.

Charlotte Suetta

A researcher in the Department of Geriatric and Palliative Medicine at Copenhagen University Hospital in Copenhagen, Denmark, who wrote an accompanying editorial.

Got photos? Submit your photos here. ›

What they’re saying

“What was surprising was the amount of muscle mass loss.”

— John Batsis, Associate Professor of Medicine

“Lean mass does not equal skeletal muscle quality function or health. There's no consistent data yet linking this loss to loss of muscular function.”

— Jaime Almandoz, Professor of Medicine and Medical Director

“The question is no longer whether incretin-based therapies reduce body weight. They do. The question now is whether we can ensure that the weight lost is predominantly fat while preserving the muscle needed for metabolic health, physical function, and healthy aging.”

— Charlotte Suetta, Researcher

What’s next

New trials should include older adults, use standardized measures of muscle-related outcomes, and include metrics of function, according to the editorial by Charlotte Suetta.

The takeaway

While weight-loss drugs have significant benefits in reducing obesity-related complications, clinicians need to be mindful of their impact on muscle mass, especially in older adults. Tracking muscle function and strength, and referring patients to physical therapists or exercise specialists, will be crucial to ensuring these medications are prescribed safely and effectively.