Short answer: Mounjaro contains tirzepatide and Wegovy contains semaglutide. Tirzepatide acts on both the GIP and GLP-1 receptors, semaglutide only on GLP-1. Both are once-weekly jabs licensed for weight management in the UK, but their dose steps differ. Which one suits you is a decision for your GP or prescriber.

Key takeaways

  • Mounjaro: tirzepatide, dual-acting (GIP and GLP-1), once a week, six steps from 2.5 mg to 15 mg.
  • Wegovy: semaglutide, GLP-1 only, once a week, five steps from 0.25 mg to the usual 2.4 mg maintenance dose.
  • Ozempic is the type 2 diabetes medicine that also contains semaglutide; for weight management, the semaglutide medicine is Wegovy.
  • In SURMOUNT-5, which compared tirzepatide with semaglutide at Wegovy doses, average weight loss after 72 weeks was greater with tirzepatide.
  • The most common side effects of both are digestive: nausea, diarrhoea and constipation.

There is no single right answer to "Mounjaro or Wegovy?". The two medicines contain different active ingredients and use different dose steps, and they suit different people for different reasons. This page puts the differences side by side; which one you use is a decision your prescriber makes based on your health.

This page is for general information only and does not replace medical advice.

The differences in one table

Mounjaro Wegovy
Active ingredient Tirzepatide Semaglutide
Receptors GIP and GLP-1 GLP-1
Manufacturer Eli Lilly Novo Nordisk
How it is given Once a week, under the skin Once a week, under the skin
Starting dose 2.5 mg for 4 weeks 0.25 mg for 4 weeks
Dose steps 2.5, 5, 7.5, 10, 12.5, 15 mg 0.25, 0.5, 1, 1.7, 2.4 mg
Maintenance dose 5, 10 or 15 mg Usually 2.4 mg (1.7 mg if 2.4 mg is not tolerated)
Missed-dose window 4 days (96 hours) 5 days
Minimum gap when changing day 3 days (72 hours) 3 days
Diabetes medicine with the same ingredient Mounjaro itself is also licensed for type 2 diabetes Ozempic

The EU also approved a higher 7.2 mg Wegovy dose in February 2026; if that applies to you, the leaflet for your product is what counts. For details on use and doses, see how to inject Mounjaro, Mounjaro dosage and Wegovy dosage.

How they work differently

Both mimic gut hormones that affect fullness, blood sugar and how quickly the stomach empties. Semaglutide binds only to the GLP-1 receptor. Tirzepatide also acts on the receptor of a second hormone, GIP, which is why it is called a "dual agonist".

Head to head: SURMOUNT-5

SURMOUNT-5, published in The New England Journal of Medicine in 2025, compared tirzepatide and semaglutide directly. It ran for 72 weeks in adults with obesity who did not have diabetes:

  • With tirzepatide (the highest tolerated dose, 10 or 15 mg), average weight loss was about 20.2%.
  • With semaglutide (1.7 or 2.4 mg, the Wegovy doses), average weight loss was about 13.7%.

Because semaglutide was used at Wegovy doses, this is the closest thing to a direct Mounjaro vs Wegovy comparison. Even so, these are averages and results varied a lot from person to person. A medicine being "more effective" on average does not make it the better fit for everyone: your medical history, other medicines, how you tolerate side effects, availability and cost all play a part.

Side effects

For both medicines, the most common side effects are digestive: nausea, diarrhoea, constipation, vomiting and reduced appetite. They tend to be more noticeable at the start and after each dose increase, and usually settle over time. More in weight-loss injection side effects.

Switching from one to the other

Whether to switch from Wegovy to Mounjaro or the other way round, including which dose the new medicine starts at, is entirely your prescriber's decision. The two are not used together.

Whichever one you use

Whichever jab you are prescribed, your prescriber will ask similar things at reviews: which day you injected, which dose you are on, how you felt and how your weight has changed. Haftra supports both medicines and keeps your injections, dose, site and symptoms in one place. It also records a switch from one medicine to another, so your history stays in one timeline. It does not suggest doses. It is free.

iPhone, iPad and Apple Watch. Free.

Frequently asked questions

What is the difference between Mounjaro and Wegovy?

Mounjaro contains tirzepatide, which acts on the GIP and GLP-1 receptors. Wegovy contains semaglutide, which acts only on GLP-1. Their dose steps and maintenance doses are also different.

Which causes more weight loss, Mounjaro or Wegovy?

In SURMOUNT-5, average weight loss after 72 weeks was about 20.2% with tirzepatide and about 13.7% with semaglutide at Wegovy doses. These are averages and individual results vary.

Can you take Mounjaro and Wegovy together?

No. They are not used together; any switch between them is made by your prescriber.

Is Wegovy the same as Ozempic?

Both contain semaglutide, but they are separate medicines: Wegovy is licensed for weight management and Ozempic for type 2 diabetes, with different dose steps. See how to use Ozempic.

Sources

  • EMA: Mounjaro (tirzepatide), summary of product characteristics
  • EMA: Wegovy (semaglutide), summary of product characteristics
  • Aronne LJ et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025.
  • MHRA (Medicines and Healthcare products Regulatory Agency)
  • NHS: Obesity treatment

Last reviewed: 26 September 2026