Short answer: Mounjaro contains tirzepatide and Ozempic contains semaglutide. Tirzepatide acts on both the GIP and GLP-1 receptors, semaglutide only on GLP-1. Both are injected once a week, but their dose steps and pens are different. Which one suits you is a decision for your doctor.

Key takeaways

  • Mounjaro: tirzepatide, dual-acting (GIP and GLP-1), once a week, six steps from 2.5 mg to 15 mg.
  • Ozempic: semaglutide, GLP-1 only, once a week, four steps from 0.25 mg to 2 mg.
  • In the US, both are approved for type 2 diabetes. The weight-management brands of the same medicines are Zepbound (tirzepatide) and Wegovy (semaglutide).
  • In SURMOUNT-5, the head-to-head trial, average weight loss after 72 weeks was greater with tirzepatide.
  • The most common side effects of both are digestive: nausea, diarrhea and constipation.

There is no single right answer to "Mounjaro or Ozempic?". The two medicines contain different active ingredients, use different dose steps and come in different pens. This page puts the differences side by side; which one you use is a decision your doctor makes based on your health.

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

The differences in one table

Mounjaro Ozempic
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, 2 mg
Pen (US) Single-dose pen, one injection per pen Multi-dose pen, new needle each time
Missed-dose window 4 days (96 hours) 5 days
Minimum gap when changing day 3 days (72 hours) 2 days (48 hours)
Weight-management brand of the same medicine Zepbound Wegovy

For details on use and doses, see how to inject Mounjaro, the Mounjaro dosage chart and how to use the Ozempic pen.

How they work differently

Both mimic gut hormones that affect fullness, blood sugar and how fast 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%.

These are averages, and results varied a lot from person to person. The trial also used semaglutide at Wegovy doses, not Ozempic doses, so in US terms it was closer to Zepbound vs Wegovy. 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, diarrhea, constipation, vomiting and reduced appetite. They tend to be more noticeable at the start and after each dose increase, and usually ease over time. More in GLP-1 injection side effects.

Switching from one to the other

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

Whichever one you use

Whatever you are prescribed, your doctor will ask similar things at check-ups: 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 Ozempic?

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

Which causes more weight loss, Mounjaro or Ozempic?

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 Ozempic together?

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

Is Ozempic approved for weight loss?

No. In the US, Ozempic is approved for type 2 diabetes. The semaglutide brand approved for weight management is Wegovy, and the tirzepatide one is Zepbound.

Sources

  • FDA - Mounjaro (tirzepatide) prescribing information
  • FDA - Ozempic (semaglutide) prescribing information
  • Aronne LJ et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025.
  • U.S. Food and Drug Administration (FDA)

Last reviewed: September 26, 2026