Wegovy or Mounjaro? Semaglutide and tirzepatide compared

Two medicines, one goal

When people ask about weight loss injections today, they usually mean one of two substances: semaglutide, approved for weight management as Wegovy, or tirzepatide, known as Mounjaro. Both mimic gut hormones released after eating and act on the regulation of hunger and fullness. Both are injected once a week and increased slowly.

The key difference is the mechanism. Semaglutide acts only on the receptor for GLP-1 (glucagon-like peptide 1). Tirzepatide also acts on the receptor for GIP (glucose-dependent insulinotropic polypeptide). This second action is considered one reason why tirzepatide produced greater weight loss in trials. Detailed profiles are in Wegovy (semaglutide 2.4 mg) and Mounjaro (tirzepatide).

The head-to-head trial: SURMOUNT-5

For a long time there were only separate trials, whose results should not simply be placed side by side because participants, duration and conditions differed. SURMOUNT-5, published in the New England Journal of Medicine in 2025, compared both directly for the first time. 751 adults with obesity but without type 2 diabetes received tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks, each at the highest tolerated dose.

The result: weight fell on average by 20.2 per cent with tirzepatide and 13.7 per cent with semaglutide. Tirzepatide was also ahead on waist circumference and on the share of people losing at least 10, 15, 20 or 25 per cent. The most common side effects in both groups were digestive, mostly mild to moderate. The trial was open-label and funded by the maker of tirzepatide; both belong to a fair assessment.

The evidence at a glance

	Semaglutide (Wegovy)	Tirzepatide (Mounjaro)
Mechanism	GLP-1 receptor agonist	GIP and GLP-1 receptor agonist
Approval trial in obesity	STEP 1: minus 14.9 % after 68 weeks	SURMOUNT-1: minus 15.0 to 20.9 % after 72 weeks
Head-to-head SURMOUNT-5	minus 13.7 % after 72 weeks	minus 20.2 % after 72 weeks
Type 2 diabetes, HbA1c after 40 weeks	minus 1.86 points (1 mg)	minus 2.01 to 2.30 points
Cardiovascular outcomes in overweight	SELECT: 20 % fewer major events	no comparable evidence in the cited sources
Sleep apnoea	no dedicated trial in the cited sources	clear fall in breathing pauses (NEJM 2024)
Weekly maintenance dose	2.4 mg	5, 10 or 15 mg

In type 2 diabetes there is also a direct comparison: tirzepatide lowered long-term blood sugar more than semaglutide 1 mg over 40 weeks (Frías and colleagues, NEJM 2021, 1,879 participants). For semaglutide, on the other hand, a benefit for the heart and blood vessels has been shown in people with overweight and existing cardiovascular disease: in SELECT, heart attack, stroke and cardiovascular death fell by 20 per cent.

Which may suit whom

There is no general answer to which is better; it depends on your starting point and goals. Points that matter in the medical assessment:

• Existing cardiovascular disease, for example after a heart attack or stroke: for semaglutide, SELECT shows fewer major events.
• Obstructive sleep apnoea with obesity: for tirzepatide, trials show a clear fall in breathing pauses.
• The largest possible weight loss as the goal: tirzepatide was superior in the direct comparison.
• Oral contraception: with tirzepatide the pill may be less reliable; the product information advises extra contraception at the start and after each dose increase.
• Tolerability and experience: if one medicine was poorly tolerated or had little effect, the other can be tried, with a fresh escalation.
• Contraindications are largely the same for both: pregnancy and breastfeeding, a history of medullary thyroid carcinoma or MEN 2, previous pancreatitis as a reason for caution.

Reading the trials correctly

Figures from different trials can only be compared to a limited extent: STEP 1 lasted 68 weeks, SURMOUNT-1 72 weeks, and participants differed in starting weight and other conditions. Keep three things in mind with any figure: they are averages, they refer to the highest tolerated dose, and they were achieved together with diet and exercise support. SURMOUNT-5 measured weight, not heart attacks or strokes; depending on your history, that difference may matter more than a few percentage points of extra weight loss.

Dosing and everyday life

Semaglutide is increased over 16 weeks in five steps from 0.25 mg to 2.4 mg a week. Tirzepatide starts at 2.5 mg and rises in 2.5 mg steps at least four weeks apart to 5, 10 or 15 mg. Missed doses can be taken up to five days late with semaglutide and up to four days late with tirzepatide. For both, weight largely returns after stopping in most people; see Stopping weight loss injections. Side effects are compared in Side effects of weight loss injections.

Costs and insurance

For weight reduction, German statutory health insurance pays for neither substance, because § 34 (1) SGB V excludes medicines for weight loss and appetite control. Private insurers decide according to the policy. Medicine costs differ by substance and dose; the pharmacy’s price is binding. The overview is in Weight loss injections.

When you need urgent medical help

Call 112 for severe upper abdominal pain radiating to the back, shortness of breath or swelling after the injection and sudden loss of vision. For ongoing vomiting or dehydration outside surgery hours, call the German on-call medical service on 116 117, and pause the next dose until a doctor has assessed you.