Mounjaro and Wegovy: two medicines, one honest comparison

Step 1, understand what each medicine actually is

The confusion between Mounjaro and Wegovy is understandable. Both are weekly self-injected pens, both sit in the GLP-1 class of medicines, and both are prescribed for weight management. That's roughly where the overlap ends.

Mounjaro's active ingredient is tirzepatide, made by Eli Lilly. It works on two receptors simultaneously: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Stimulating both pathways slows how quickly the stomach empties, signals fullness to the brain, and influences blood-sugar regulation. It is the only dual-agonist weight-loss medicine currently licensed in the UK. You can read the NHS overview of tirzepatide for a plain-English account of how it works and what to expect.

Wegovy's active ingredient is semaglutide, made by Novo Nordisk, and if you want a full picture of what Wegovy is, how it works, and what to expect from treatment, our dedicated page covers all of that in detail. It targets the GLP-1 receptor alone. That single pathway still produces meaningful appetite reduction and slowed gastric emptying, semaglutide is well-studied and the trial record is substantial. But the receptor profile is narrower. The NHS semaglutide page covers the practical details patients most often ask about. Worth noting: Ozempic is also semaglutide, but licensed for type 2 diabetes rather than weight management. The two brand names are not interchangeable for this purpose.

So when people ask whether Wegovy or Mounjaro is the right choice, they are choosing between a single-receptor and a dual-receptor medicine. That distinction matters when the evidence is examined.

Step 2, look at what the trial evidence actually shows

Both medicines have solid phase-3 trial programmes behind them, and both produced results well beyond what diet and lifestyle changes typically achieve alone.

In the SURMOUNT-1 trial, tirzepatide at the highest dose (15 mg) produced an average body-weight reduction of around 20–21% over 72 weeks in adults with obesity. The STEP 1 trial for semaglutide 2.4 mg (the standard maintenance dose for Wegovy) showed an average reduction of around 15% over 68 weeks. Those are different trial populations and different study designs, so a direct comparison from those figures alone would be imprecise.

The more relevant data point is the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025. This was a direct head-to-head study in 751 adults with obesity and without diabetes, running for 72 weeks. Tirzepatide produced greater average weight loss than semaglutide 2.4 mg. NICE's committee discussion notes in TA1026 also reference indirect comparisons that favour tirzepatide. Novo Nordisk has since developed a 7.2 mg dose of semaglutide (approved by the MHRA in early 2026) with trial results approaching tirzepatide 15 mg, which narrows the gap. For a closer look at how the two medicines sit against each other on specific numbers, our detailed evidence comparison covers this in full.

Neither result is a guarantee. Trial averages describe populations; individual outcomes vary, and a prescriber considers the whole clinical picture rather than a single headline statistic.

Step 3, check what each medicine is licensed for and who qualifies

Both Mounjaro and Wegovy share the same core licensed population for weight management: adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as hypertension, high cholesterol, obstructive sleep apnoea, prediabetes, or type 2 diabetes. Lower BMI thresholds can apply for some ethnic backgrounds under UK guidance. BMI alone never determines the outcome, a prescriber assesses the full picture, including your medical history, current medicines, and any contraindications.

Neither medicine is licensed for use under the age of 18. Both are contraindicated during pregnancy and breastfeeding, and should not be used if you are trying to conceive. Women taking oral contraceptives who start Mounjaro specifically should add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide's effect on gastric emptying may reduce pill absorption, there is no equivalent evidence for semaglutide in this regard.

On the NHS, eligibility for each medicine follows stricter and separate criteria than the licensed indications, access is phased, waiting lists can be long, and not every GP practice participates yet. For anyone who doesn't meet the current NHS thresholds or doesn't want to wait, private treatment through a regulated online pharmacy is the legal alternative. You can explore the treatment options available through a private prescription on our weight-loss overview page, and see how private costs are structured on the Wegovy cost page.

Step 4, understand how the choice is made in practice

This is the part most online comparisons skip. Reading about Mounjaro and Wegovy side by side is useful context, but the decision isn't one you make alone, it's a clinical conversation. A prescriber considers your medical history, any medicines you already take, your BMI and any relevant conditions, your preferences around administration, and what, if anything, you've tried before.

There are situations where one medicine is more clinically appropriate than the other. Someone with a history of pancreatitis, for instance, would need careful assessment before starting either. Someone switching from a previous GLP-1 treatment would be reviewed differently from someone starting for the first time. Dose titration schedules also differ: Mounjaro starts at 2.5 mg and is increased by the prescriber at roughly four-week intervals; Wegovy begins at 0.25 mg and follows its own stepped schedule up to 2.4 mg (or 7.2 mg for eligible patients).

It is worth addressing a misconception gently here: some people arrive at this comparison wondering whether Wegovy and Mounjaro are actually the same medicine, and the short answer is that they are not. These are distinct molecules with different receptor targets, made by different manufacturers, with separate clinical trial programmes. The fact that both slow gastric emptying and both reduce appetite can make them feel equivalent from the outside, but a closer look at whether Manjaro and Wegovy are the same makes clear why the distinction matters clinically, and why choosing between Wegovy or Mounjaro is a decision worth making carefully with a prescriber. The right choice genuinely depends on the individual.

If you'd like to understand whether you're eligible and which medicine might suit your situation, check your eligibility with our prescribers, it's a free consultation, reviewed the same day by a real clinician, not an automated system. Our clinical team can answer questions that a comparison article simply can't.