What is tirzepatide used for?

What each approval rests on

• Type 2 diabetes — the SURPASS programme, which reported A1C reductions of 2.0–2.5%, supporting the Mounjaro approval in May 2022.
• Chronic weight management — the SURMOUNT programme. SURMOUNT-1 reported average weight loss of 20.9% at 15 mg over 72 weeks, supporting the Zepbound approval in November 2023.
• Obstructive sleep apnea — SURMOUNT-OSA, which reported reductions in apnea severity and supported a December 2024 label expansion. This one is worth noting because it is an approval for a condition rather than for weight itself.

The head-to-head result

SURMOUNT-5 randomised tirzepatide against semaglutide in the same study and reported 20.2% average weight loss against 13.7%. That is the rare directly comparative figure in this field. It should be read as what it is: one trial, one population, one pair of dose ceilings — not a general ranking of the two molecules across every use.

What is still running

SURPASS-CVOT is an ongoing cardiovascular outcomes trial in people with type 2 diabetes and established cardiovascular disease. A post-hoc analysis of SURMOUNT-5 projected greater ten-year cardiovascular risk reduction with tirzepatide than semaglutide, and a projection from a post-hoc analysis is a hypothesis rather than an outcome. Metabolic liver disease and heart failure are also under investigation.

What dual agonism explains, and what it does not

Tirzepatide engages both the GLP-1 and GIP receptors where semaglutide engages GLP-1 alone, and that second arm is the usual explanation offered for the larger weight figures. The mechanism is real and the difference in results is measured. The step that does not follow is treating a mechanistic difference as a general prediction: the head-to-head advantage was measured on weight, in one trial, and does not automatically extend to indications neither compound has been compared on.