The difference between Ozempic and Mounjaro for weight loss

The licensing question: why this is the first thing to settle

The most important difference between Ozempic and Mounjaro is not the molecule or the trial data. It is what each medicine is formally authorised to treat in the UK.

Ozempic contains semaglutide at doses of 0.5 mg, 1 mg and 2 mg. The MHRA licenses it solely for type 2 diabetes. If a doctor prescribes it for weight management, that is an off-licence use, legal but requiring individual clinical justification, and explicitly outside the scope of products like Wegovy, which uses the same active ingredient at a higher 2.4 mg maintenance dose specifically developed and licensed for weight loss. The NHS medicines page for semaglutide sets this out plainly.

Mounjaro, by contrast, holds dual UK licences: one for type 2 diabetes and one for weight management in adults with a BMI of 30 or above, or 27 or above alongside a weight-related condition such as high blood pressure or obstructive sleep apnoea. That makes it the straightforward on-licence route when weight loss is what someone is seeking. You can read more about how these products sit alongside each other on our Mounjaro vs Ozempic overview.

At nume, our prescribers do not supply Ozempic for weight management. The products dispensed for weight loss are Mounjaro and Wegovy. This page explains the comparison; our weight-loss treatment overview covers what we do offer.

How the two medicines actually work, and where they differ

Ozempic is a GLP-1 receptor agonist. It mimics glucagon-like peptide-1, a gut hormone that tells the pancreas to release insulin in response to food, slows gastric emptying and reduces appetite signals in the brain. That single-pathway action is well understood and underpins a large body of diabetes trial data.

Mounjaro activates two receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). GIP is a second gut hormone involved in both insulin secretion and fat metabolism. Activating both simultaneously appears to produce stronger appetite suppression and greater metabolic effects than GLP-1 alone. Mounjaro is currently the only dual GIP/GLP-1 receptor agonist licensed in the UK.

In the SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks), tirzepatide at 15 mg produced an average body-weight reduction of around 20–21%, as published in the New England Journal of Medicine. The SURMOUNT-5 head-to-head trial, also published in the NEJM in 2025, found tirzepatide produced greater average weight loss than semaglutide 2.4 mg (Wegovy) over 72 weeks, not Ozempic, which was not studied head-to-head in that trial. If you want to understand what makes Mounjaro and Ozempic different at a mechanistic level, our dedicated page works through the science in plain terms. Comparing Ozempic's diabetes-dose data with Mounjaro's weight-loss data is therefore not straightforward, and any side-by-side figure should be read cautiously.

For a fuller breakdown of how the semaglutide weight-loss product compares with Mounjaro, our page on the difference between Mounjaro and Wegovy goes into the evidence in more detail.

Side effects, eligibility and what to expect in practice

The side-effect profile of both medicines is broadly similar because both slow gastric emptying. Nausea, loose stools, constipation, reflux and fatigue are the most commonly reported effects, typically most noticeable after a new dose begins and settling over days to a couple of weeks. Injection-site reactions occur with both. The NHS tirzepatide page lists Mounjaro's full side-effect profile; the equivalent semaglutide page covers Ozempic and Wegovy together.

In January 2026 the MHRA issued a Drug Safety Update highlighting acute pancreatitis as an infrequent but serious risk with GLP-1 medicines: severe stomach pain that spreads to the back, with or without vomiting, requires urgent medical attention. That applies to both Ozempic and Mounjaro.

There is one practical difference worth noting for women. Women taking oral contraceptive pills who start Mounjaro should use an additional non-oral contraceptive method for the first four weeks of treatment and for four weeks after each dose increase, because slowed gastric emptying can reduce pill absorption. NHS guidance does not flag the same concern for semaglutide. Discuss this with a prescriber before starting either medicine.

On eligibility: Mounjaro's weight-management licence covers BMI 30-plus, or 27-plus with a qualifying condition. Because Ozempic carries no weight-management licence, there is no equivalent on-licence eligibility threshold for that purpose. Our guide to the key differences between Ozempic and Mounjaro covers eligibility, licensing and prescribing considerations in more depth. Anyone considering weight management treatment should also check our consultation page, where a prescriber reviews your situation individually.

A quick comparison at a glance

Which of the two licensed weight-loss medicines (Mounjaro or Wegovy) is right for you is a clinical decision, one that depends on your medical history, any other medicines you take, your BMI and your preferences. Our clinical team reviews every consultation personally. If cost is part of your thinking, the Mounjaro and Wegovy price comparison covers what private treatment typically costs and what those prices include. For a deeper look at how the licensed weight-loss products sit alongside each other, see our guide to what separates Wegovy from Mounjaro. Speak to our prescribers to work through which option fits your circumstances.