Semaglutide
A long-acting GLP-1 receptor agonist approved in injectable form for type 2 diabetes (Ozempic) and chronic weight management (Wegovy), and in oral form (Rybelsus). It is among the most extensively studied molecules in the peptide space.
Tirzepatide
A first-in-class dual agonist of the GIP and GLP-1 receptors, approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management. Its dual mechanism delivers some of the largest weight reductions reported in registrational obesity trials.
Mechanism
Semaglutide is a selective GLP-1 receptor agonist with a week-long half-life. Tirzepatide activates both GLP-1 and GIP receptors. The GIP component is proposed to add adipose-insulin-sensitivity and energy-handling effects, though the incremental contribution in humans is still debated.
Trial results
STEP 1 reported 14.9% mean weight reduction with semaglutide 2.4 mg over 68 weeks. SURMOUNT-1 reported 20.9% with the highest tirzepatide dose over 72 weeks. Cross-trial comparisons are imperfect — populations and designs differ — but the directional difference is consistent across head-to-head-adjacent data.
Safety
Both carry gastrointestinal effects as the dominant tolerability issue, both warn on gallbladder disease and pancreatitis, and both share the medullary thyroid carcinoma/MEN2 contraindication. Tirzepatide adds hypoglycemia caution when combined with insulin secretagogues.
Practical differences
Both are weekly injectables (semaglutide additionally has an oral formulation). Access, insurance coverage, and labeled indications differ by jurisdiction; the choice between them is a clinical decision, not a catalog decision.
Frequently Asked Questions
Can I switch from one to the other?
Switching approved incretin medicines is a real clinical practice — but it is managed by prescribers with dose-transition plans, not by catalog research.
Why do SURMOUNT results look so much larger than STEP results?
Part mechanism, part trial design: different populations, durations, and dose-escalation schemes. Head-to-head trials give cleaner answers than cross-trial comparisons.
Evidence tier: Approved medicine · Last reviewed: 2026-09-05 · Sources cited below.