Drug facts
Semaglutide and muscle loss
Quick answer
The label does not answer it. “Lean body mass”, “body composition” and “sarcopenia” appear zero times in the full published label, and the only two mentions of “muscle” are an instruction not to inject into one. What is established is total weight loss.
What the label measures1
Body weight, as a percentage change and in kilograms, and the share of participants crossing thresholds like 5% and 10%. Those are the endpoints the trials were built around — see STEP 1 — and they count every kilogram the same, whatever tissue it came from.
What it does not measure1
Composition. A weight endpoint cannot distinguish fat from lean mass, and this label reports no measurement that does. So the honest answer to “how much of it is muscle” is that this document does not say, and neither does any figure derived from it.
It is well established that weight loss from any cause — diet, surgery, illness — includes lean tissue as well as fat. That is general physiology rather than something this label establishes about this drug, and a page quoting a precise percentage for semaglutide specifically is quoting something that is not here.
Why the question matters anyway1
Because it is the question behind what happens when the drug stops. STEP 4 found weight returning after withdrawal; what returns and what was lost need not be the same tissue. That is a real concern, and it is one the published label leaves open rather than settles.
What this page is not
It is not exercise or nutrition advice, and it does not tell you what is happening to your own body. It reports a documented absence.
Sources
- FDA prescribing information for WEGOVY (semaglutide), full label as published on DailyMed, revision 6/2026 — complete text searched (212,786 characters) DailyMed