Reference, not advice. Semaglutide and tirzepatide are prescription medicines. This page describes what the evidence shows. It publishes no doses, gives no guidance on use, and does not replace a prescriber. Vallydia does not sell, supply or link to any GLP-1 medicine.
On weight, tirzepatide wins. This is not a cross-trial guess: it comes from a direct comparison. In SURMOUNT-5, the only head-to-head obesity trial, tirzepatide produced a mean weight loss of 20.2%, against 13.7% for semaglutide.
But "loses more weight" is not the same as "better on every outcome". The two register entries are graded A on different outcomes.
Tirzepatide is a different molecule, not a stronger version of the same one. It is a 39-amino-acid peptide that activates both natural incretin receptors, GIP and GLP-1. Semaglutide activates GLP-1 alone. Combining the two pathways gives a larger effect on glucose and on weight than GLP-1 alone. That is a pharmacological difference, not a difference in dose.
| Trial | Population | Semaglutide | Tirzepatide |
|---|---|---|---|
| SURMOUNT-5 | Obesity | −13.7% body weight | −20.2% body weight |
| SURPASS-2 | Type 2 diabetes | HbA1c reduction | Greater HbA1c reduction |
Why does semaglutide show 13.7% here when it is often cited at "about 15%"? The 15% comes from its own STEP programme, in a different population and design. Head-to-head trials are the only fair comparison. Cross-trial numbers suggest a direction, and a direct trial measures the gap.
| Outcome | Semaglutide | Tirzepatide |
|---|---|---|
| Glycaemic control in type 2 diabetes | A (SUSTAIN) | A (SURPASS) |
| Weight management in obesity | A (STEP, ~15%) | A (SURMOUNT, ~20–22%) |
| Cardiovascular risk reduction | A (SELECT, SOUL; vs placebo) | A (SURPASS-CVOT; vs dulaglutide, type 2 diabetes) |
| Kidney outcomes in type 2 diabetes with CKD | A (FLOW) | Not graded |
| Obstructive sleep apnea with obesity | Not graded | A (SURMOUNT-OSA) |
"Not graded" does not mean "doesn't work". It means the register has no graded outcome here because no approved, completed outcome programme sits behind one. Both now carry a cardiovascular grade, but they earned it differently. Semaglutide's comes from placebo-controlled trials (SELECT, SOUL). Tirzepatide's comes from SURPASS-CVOT, approved in August 2026: in type 2 diabetes with established cardiovascular disease, it had an 8% lower rate of major cardiovascular events than dulaglutide, another GLP-1 drug, and 16% fewer deaths from any cause. Semaglutide still has a kidney outcome (FLOW) that tirzepatide does not. Tirzepatide has the larger effect on weight and an approval for sleep apnea, the first drug approved for that condition.
| Semaglutide | Tirzepatide | |
|---|---|---|
| Brands | Ozempic, Wegovy, Rybelsus | Mounjaro, Zepbound |
| Manufacturer | Novo Nordisk | Eli Lilly |
| Receptors | GLP-1 | GIP + GLP-1 |
| Forms | Weekly injection, daily tablet | Weekly injection |
| Weight (head-to-head, SURMOUNT-5) | −13.7% | −20.2% |
| Cardiovascular outcome | Yes (vs placebo) | Yes (vs dulaglutide, type 2 diabetes) |
| Kidney outcome | Yes (FLOW) | Not graded |
| Sleep apnea approval | No | Yes |
Larger and faster weight loss can bring more visible change in the face: hollowing, laxity and lines. This is an appearance effect of rapid weight loss, not a property of either molecule. See Skincare on GLP-1s – "Ozempic face".
Is tirzepatide more effective than semaglutide? For weight, yes, by direct comparison: 20.2% against 13.7% in SURMOUNT-5. For glucose control, SURPASS-2 also favoured tirzepatide.
Does tirzepatide protect the heart? In type 2 diabetes with established cardiovascular disease, yes: SURPASS-CVOT showed an 8% lower rate of major cardiovascular events than dulaglutide, and the FDA approved that use in August 2026 (grade A). Semaglutide's cardiovascular grade rests on placebo-controlled trials (SELECT, SOUL).
Is Mounjaro the same as Zepbound? Yes. Both contain tirzepatide. Mounjaro is approved for type 2 diabetes, and Zepbound for obesity and obstructive sleep apnea. Brand naming varies by market.
How do they compare with liraglutide? Both outperform it on weight. See Victoza vs Saxenda and Ozempic vs Wegovy.
Does Vallydia publish doses? No. Dosing is a prescriber's decision.
On weight, there is no contest: the one direct trial favours tirzepatide by about six and a half percentage points. Beyond weight and glucose, the picture is closer than it was. Both now carry a graded cardiovascular outcome, semaglutide against placebo and tirzepatide against an active comparator, and only semaglutide has a graded kidney outcome. Which is "better" depends on which outcome the question is about.
One receptor or two. The trial you read decides which answer you get.
Vallydia does not sell, supply or link to any GLP-1 medicine.
How we separate evidence levels: how we grade · how we grade.
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