Semaglutide vs Tirzepatide: What the Head-to-Head Trials Show

By Evan Marsh, EditorUpdated August 8, 2026Sources: SURMOUNT-5 and SURPASS-2, both direct comparisons

Almost every comparison of these two drugs is built the wrong way — by putting STEP-1's number next to SURMOUNT-1's number, two separate trials with different populations and durations. That estimate is unnecessary here, because unlike most pairings in this class, semaglutide and tirzepatide have been tested against each other. Twice.

The head-to-head result

SURMOUNT-5 randomized 751 adults with obesity and without type 2 diabetes to maximum tolerated tirzepatide (10 or 15 mg) or maximum tolerated semaglutide (1.7 or 2.4 mg), for 72 weeks, published in the New England Journal of Medicine:

Outcome at 72 weeks	Tirzepatide	Semaglutide
Mean body-weight change	−20.2% (95% CI −21.4 to −19.1)	−13.7% (95% CI −14.9 to −12.6)
Waist circumference	−18.4 cm	−13.0 cm
Reaching ≥10%, ≥15%, ≥20%, ≥25% loss	More likely	Less likely

Mean body-weight reduction — both arms from the same trial, SURMOUNT-5

InvestigationalFDA approved

TirzepatideSURMOUNT-5, 72 weeks

20.2%

SemaglutideSURMOUNT-5, 72 weeks

13.7%

Why this page does not need an estimand disclaimer. Everywhere else on this site we warn that obesity trials report results twice and that mixing conventions inflates one drug's lead. That problem disappears in a head-to-head: both arms were randomized in the same trial, measured the same way, over the same 72 weeks. A single direct trial outranks any table we could assemble — including our ownclass comparison, which necessarily estimates across trials.

The comparison in type 2 diabetes

SURPASS-2 ran the same exercise in 1,879 people with type 2 diabetes over 40 weeks, comparing three tirzepatide doses against semaglutide 1 mg:

Arm	HbA1c change	Additional weight loss vs semaglutide
Tirzepatide 5 mg	−2.01 points	−1.9 kg
Tirzepatide 10 mg	−2.24 points	−3.6 kg
Tirzepatide 15 mg	−2.30 points	−5.5 kg
Semaglutide 1 mg	−1.86 points	—

One caveat that matters and is usually dropped: the comparator was semaglutide1 mg, the type 2 diabetes dose. The obesity dose is 2.4 mg. SURPASS-2 is a fair test of the diabetes question and an unfair one for the weight question — which is precisely why SURMOUNT-5 was run.

Where semaglutide wins

If the comparison stopped at the scale, this page would be one paragraph long. It does not, because the two drugs have different approved indications, and the difference runs the other way:

	Semaglutide	Tirzepatide
Receptors	GLP-1	GIP + GLP-1
Brands	Wegovy, Ozempic, Rybelsus	Zepbound, Mounjaro
Cardiovascular outcomes	Approved to reduce major adverse cardiovascular events	Not approved for this
Liver disease	Noncirrhotic MASH with fibrosis (accelerated approval)	Not approved for this
Sleep apnea	Not approved for this	Moderate-to-severe OSA in adults with obesity
Oral formulation	Yes	No
Dose range	0.25–2.4 mg weekly (Wegovy)	2.5–15 mg weekly

Cardiovascular outcome evidence is the highest tier available in this field: it describes what happened to people, not what happened to a number. Semaglutide has it and tirzepatide does not. Anyone choosing on weight alone is optimizing the surrogate and ignoring the endpoint.

Tolerability

Both drugs are defined by gastrointestinal effects — nausea, diarrhea, vomiting, constipation — worst during escalation and generally settling at a stable dose. Both labels carry the boxed warning for thyroid C-cell tumors seen in rodents, with contraindications for personal or family history of medullary thyroid carcinoma or MEN 2, plus pancreatitis and gallbladder cautions.

The interesting finding from SURMOUNT-5 is what did not happen: safety results were broadly consistent between arms. Adding a receptor produced a substantially larger effect without a proportionally larger adverse-event burden, which is unusual and is part of why GIP agonism attracted so much interest.

Practical differences

Both are prescribable. Unlike retatrutide, neither requires a gray-market route — this is a conversation to have with a physician, not a sourcing problem.
Both cost roughly $1,000–1,300 monthly at list, with manufacturer savings programs bringing real-world cost well below that.
Semaglutide has an oral option, which matters more than it sounds for anyone who will not inject.
Weight returns after stopping either one. The STEP-1 extension documented substantial regain after semaglutide withdrawal, and nothing suggests tirzepatide behaves differently. These treat a chronic condition; they are not a course with an endpoint.

The honest summary

For weight reduction, tirzepatide, and the evidence is direct rather than inferred. For demonstrated cardiovascular benefit, semaglutide, and nothing tirzepatide has published changes that. For most people the choice is made by indication, insurance and tolerability rather than by a percentage — and that choice belongs with a physician who knows the rest of the medical history.

Frequently asked questions

Is tirzepatide better than semaglutide for weight loss?

In the one trial that tested them head to head, yes. SURMOUNT-5 randomized 751 adults with obesity to one drug or the other for 72 weeks: tirzepatide produced a 20.2% mean weight reduction against semaglutide's 13.7%. That is a direct comparison, not an estimate assembled from two separate trials.

What is the difference between semaglutide and tirzepatide?

Semaglutide activates one receptor, GLP-1. Tirzepatide activates two, GIP and GLP-1. The second receptor is the reason for the larger weight and glycemic effects, and it may also explain the comparable-or-better tolerability, which is not what adding a mechanism usually does.

Which one has better outcome data?

Semaglutide. It is approved to reduce the risk of major adverse cardiovascular events in adults with established cardiovascular disease and obesity, and it carries an accelerated approval in noncirrhotic MASH with fibrosis. Tirzepatide is approved for obstructive sleep apnea in adults with obesity. Neither weight figure captures this difference.

Which is better for type 2 diabetes?

SURPASS-2 compared them directly over 40 weeks: HbA1c fell 2.01 to 2.30 percentage points across tirzepatide doses versus 1.86 on semaglutide 1 mg, with 1.9 to 5.5 kg more weight loss. Note the comparator was semaglutide 1 mg, the diabetes dose, not the 2.4 mg obesity dose.

Do the side effects differ?

Both are dominated by gastrointestinal effects concentrated during dose escalation, and both carry the class boxed warning for thyroid C-cell tumors observed in rodents. In SURMOUNT-5 the safety profiles were broadly consistent between arms — the larger effect from tirzepatide did not come with a proportionally larger adverse-event burden.

Sources

Aronne LJ et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). New England Journal of Medicine, 2025. PubMed
Frías JP et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). New England Journal of Medicine, 2021;385(6):503–515. PubMed
Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022;387(3):205–216. PubMed
Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). New England Journal of Medicine, 2021;384(11):989–1002. PubMed
Wilding JPH et al. Weight regain after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022;24(8):1553–1564. PubMed
Labels: Wegovy (semaglutide) · Zepbound (tirzepatide)

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Not medical advice. Both are approved prescription medicines. Decisions about them belong with a licensed physician who knows your medical history.