Semaglutide vs Tirzepatide: what actually differs?
Both therapies have mature human evidence and can produce substantial weight loss. The useful comparison goes beyond one headline number to mechanism, body composition, lean-mass evidence and clinical maturity.
Mechanism
Semaglutide is a GLP-1 receptor agonist. Tirzepatide activates both GLP-1 and GIP receptors. Different mechanisms do not automatically mean better outcomes, but they help explain why the clinical programs are not interchangeable.
Weight-loss evidence
Both have strong randomized human evidence. Tirzepatide has generally produced greater average weight loss in major obesity trials, while semaglutide has a longer track record and broad clinical experience.
Body composition and lean mass
Both can reduce fat mass substantially, and both can also be accompanied by lean-mass loss. The key question is the proportion and functional significance of that change, not simply whether lean mass decreased at all.
Evidence maturity
Both sit at the mature end of the RecompSignal evidence scale for approved obesity treatment. Claim-specific maturity can still differ for narrower questions such as direct muscle preservation.
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Source approach
RecompSignal prioritizes peer-reviewed human trials, regulatory sources and direct body-composition measurements when available. This page is an educational synthesis, not individualized medical advice.
Direct evidence: SURMOUNT-5
In a randomized, open-label trial of 751 adults without diabetes, mean weight reduction at 72 weeks was 20.2% with tirzepatide versus 13.7% with semaglutide (treatment-regimen estimand). Maximum tolerated weekly subcutaneous doses were tirzepatide 10/15 mg and semaglutide 1.7/2.4 mg.
This comparison did not test oral semaglutide or 7.2 mg semaglutide and does not establish superior muscle preservation. Gastrointestinal adverse events were common; the trial was not powered for comparative safety.
What actually differs?
The short video introduces the comparison. Use the Signal Cards for source-labeled therapy evidence and the methodology page for how maturity and outcome strength are assigned.