Do GLP-1s Cause Muscle Loss? Trial DEXA Data (Philippines)

Do GLP-1 medicines make you lose muscle? It is a common question among Filipinos researching them. Weight loss means losing fat and some lean mass. Trials measure this with a DEXA scan.

Lean mass means muscle, plus water, organs and connective tissue. The mechanism is energy deficit: GLP-1 drugs cut appetite, so the body draws on both fat and lean tissue. In a DEXA substudy of STEP 1, reported in 2021, about 39 to 40 percent of weight lost on semaglutide was lean mass. In the SURMOUNT-1 DEXA substudy, published in 2025, about a quarter was lean mass on tirzepatide, a similar split to placebo.

Across studies, lean mass made up 20 to 50 percent of weight lost, similar to dieting or bariatric surgery. Why it matters: muscle drives metabolism, blood sugar control and strength. Older adults already lose lean mass with age. A 2025 joint advisory from four US obesity and nutrition groups listed adequate protein and strength training as priorities to preserve lean mass.

More research is needed. Drugs to spare muscle are in trials. In a 2026 phase 2 trial, adding bimagrumab to semaglutide meant about 92 percent of weight lost was fat, versus about 71 percent on semaglutide alone. None are approved.

With tirzepatide now in Philippine drugstores, this data matters here too. If you are sourcing research peptides in the Philippines, Primara Labs publishes independent lab reports you can verify yourself. Guides at primaralabs.com.