Do GLP-1 drugs make you lose muscle?

Some, the way any large weight loss does. In the tirzepatide trial’s scan study, about a quarter of the weight people lost was lean mass, the same share as in the placebo group, who lost weight on diet and exercise advice. The drugs cause more loss, so more lean mass goes in pounds. Lifting and protein are how you keep it.

The numbers from the trials

Lean mass counts everything that isn’t fat or bone, including water, organs and skin, so muscle is only part of it. The 2025 nutrition advisory from four US societies makes the same point.

There’s a hopeful sign too. In SEMALEAN, a year-long study of 106 adults with severe obesity on semaglutide, lean mass fell about 7 pounds (3 kg) by month seven and then held steady, while hand grip strength rose by about 9 pounds (4 kg).

Why it happens

Eating far less means less protein and less fuel coming in, and muscle that isn’t being worked hard is the tissue the body lets go. Lifting on a GLP-1 is like putting a keep sticker on your muscle before the movers arrive.

What to do

• Lift at least two or three days a week. The 2025 advisory suggests strength training at least three times a week, plus at least 150 minutes of moderate cardio.
• Eat your protein first at each meal. The advisory suggests about 1.5 g per kg of lean mass, or 80 to 120 grams a day. Under 1.2 g per kg of body weight is too low for most people. Find your range.
• Track strength and waist, not just the scale.
• Talk with your prescriber if you can’t eat enough or you’re losing fast. Never change a dose on your own.

The drug pages have the trial details: Ozempic and Wegovy, Mounjaro and Zepbound.