Tirzepatide vs semaglutide

Which produces more weight loss, and at what cost?

Direct head-to-head trial exists
In one paragraphIn the only direct trial, tirzepatide beat semaglutide: 20.2% versus 13.7% average weight loss over 72 weeks in 751 adults, with a larger drop in waist size and fewer people stopping for gut side effects. Semaglutide has the longer track record and a completed cardiovascular-outcomes trial in people without diabetes. Both are prescription medicines with the same class of side effects.

Side by side

A TirzepatideA Semaglutide
LYO grade (weight)AA
Head-to-head weight loss, 72 wkSURMOUNT-5, n=751−20.2% (22.8 kg)−13.7% (15.0 kg)
Waist circumference, 72 wkSURMOUNT-5−18.4 cm−13.0 cm
Own placebo-controlled trial−20.9% at 72 wk (SURMOUNT-1)−14.9% at 68 wk (STEP 1)
ReceptorsGIP + GLP-1GLP-1
Cardiovascular outcomes trialNon-inferior to dulaglutide in type 2 diabetes (SURPASS-CVOT, 2025)20% relative MACE reduction vs placebo in obesity without diabetes (SELECT)
Stopped for GI side effects (head-to-head)SURMOUNT-52.7%5.6%
Approved forType 2 diabetes, weight management, sleep apnoeaType 2 diabetes, weight management, cardiovascular risk reduction
First approval20222017
Verdict

Tirzepatide for weight loss, on direct evidence. Semaglutide for the most complete safety and cardiovascular record. The gap is real but individual response varies more than the averages suggest.

What the head-to-head actually showed

SURMOUNT-5 randomised 751 adults with obesity but without diabetes to the highest tolerated dose of either drug for 72 weeks. Tirzepatide produced 6.5 percentage points more weight loss on average, and a larger share of participants reached the 15%, 20% and 25% thresholds. Waist circumference fell more too.

Two details matter for reading the result. First, semaglutide was dosed at 2.4 mg, its full obesity dose, so this is not a hobbled comparator. Second, the trial was open-label — participants knew which drug they were on — which is a limitation on softer endpoints but not on a scale.

Where semaglutide still leads

Semaglutide has the SELECT trial: 17,604 adults with cardiovascular disease and no diabetes, and a 20% relative reduction in heart attacks, strokes and cardiovascular death against placebo. Tirzepatide's outcomes trial compared it to another GLP-1 drug in people with diabetes and showed non-inferiority rather than a placebo-controlled benefit. If cardiovascular protection is the goal, semaglutide's evidence is more direct — for now.

It also has five more years on the market, which matters for rare side effects that trials are too small to catch.

Side effects

The two drugs share a profile: nausea, diarrhoea, vomiting and constipation, concentrated in the dose-escalation months, plus rare pancreatitis and gallbladder events and the rodent-derived thyroid C-cell warning. In the head-to-head, fewer people on tirzepatide stopped because of gut symptoms, which is consistent with the idea that the GIP component tempers nausea, though the mechanism is not settled.

Questions people actually ask

Is tirzepatide just a stronger semaglutide?
No — it acts on an additional receptor (GIP), and it is a different molecule built on a different hormone backbone. The larger weight loss is a class difference, not a dose difference.
Can you switch from semaglutide to tirzepatide?
That is a prescribing decision, made with a clinician, and outside what this site covers. The trials that inform it exist; this page summarises them.
Which has fewer side effects?
In the head-to-head, fewer people stopped tirzepatide for gut side effects (2.7% vs 5.6%). Overall rates of nausea and diarrhoea were broadly similar between the two.

References

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