Wegovy and Mounjaro: which is better for weight loss?

What the SURMOUNT-5 head-to-head found

For most of the GLP-1 era, comparing Mounjaro and Wegovy meant putting separate trials next to each other and noting the caveats. SURMOUNT-5 changed that. The trial randomised 751 adults with obesity and no type 2 diabetes to either tirzepatide or semaglutide 2.4mg over 72 weeks, and the result favoured tirzepatide: greater average body-weight reduction and a higher proportion of participants reaching the 15%, 20% and 25% weight-loss thresholds. A closer look at the head-to-head data sets out the figures in full.

The biological reason is reasonably well understood. Wegovy acts on one receptor, the GLP-1 pathway, which regulates appetite and slows stomach emptying. Mounjaro activates both GLP-1 and GIP receptors, a dual mechanism that appears to produce a stronger effect on appetite and body weight in most people. It is the only dual-agonist weight-loss medicine licensed in the UK. This page on semaglutide versus tirzepatide covers the mechanism in more detail if you want the pharmacology without the brand names.

One important caveat: the SURMOUNT-5 comparison was against semaglutide at 2.4mg, which was the standard Wegovy maintenance dose. The MHRA approved a higher 7.2mg maintenance dose in January 2026, and a dedicated single-dose 7.2mg pen in April 2026. Trials at 7.2mg reported average weight loss of around 20.7% over 72 weeks, which narrows the gap with tirzepatide's highest doses considerably. That higher-dose data is still newer, so most clinicians compare the two medicines using the longer evidence base at 2.4mg.

Do the side-effect profiles differ in ways that matter?

Both medicines share a broadly similar side-effect picture: nausea, loose stools, constipation, indigestion and fatigue are the most frequently reported, particularly around dose increases. These are typically at their worst in the first few weeks of a new dose and ease off for most people.

There are some reported differences in the rates and character of gastrointestinal effects between the two, though direct comparison is difficult because the trials measured slightly different things. What is consistent across both is the MHRA's guidance on pancreatitis: severe stomach pain that radiates to the back (with or without vomiting) is a reason to stop the medicine and get medical help the same day. The MHRA Yellow Card scheme is the right place to report any suspected side effect from either medicine.

One difference that is specific to Mounjaro and worth knowing: because tirzepatide slows gastric emptying more markedly, NHS guidance recommends that women taking the oral contraceptive pill add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase. The equivalent concern has not been identified for semaglutide. The safety comparison page covers this (and the surgery and HRT points) in full.

Eligibility and what each NICE recommendation actually says

A question our prescribers hear most weeks is whether having been on Wegovy means you automatically qualify to switch to Mounjaro, or vice versa. The honest answer is that the NICE recommendations set different conditions.

NICE TA1026 recommends tirzepatide for adults with a BMI of at least 35 plus one or more weight-related comorbidities on the NHS, with lower thresholds of 2.5 kg/m² for some ethnic backgrounds. NICE's appraisal of tirzepatide (TA1026) sets out the criteria in full. NICE TA875 recommends semaglutide within specialist weight management services for a maximum of two years, under similar BMI criteria.

Private eligibility is broader for both: adults with a BMI of 30 or above, or 27 or above with a weight-related condition such as high blood pressure, high cholesterol, type 2 diabetes or obstructive sleep apnoea. But BMI alone doesn't decide things. A prescriber looks at your full picture: other medicines, health history, previous treatment, how you responded to the last pen. That assessment is what makes the recommendation valid. You can explore what that process looks like at our treatment consultation page.

Cost: why Mounjaro typically costs more

The short version is that Mounjaro is generally more expensive than Wegovy in the UK private market, partly because of Eli Lilly's list pricing (which rose significantly from September 2025) and partly because of supply dynamics. Typical private prices since that change have ranged roughly £149–£375 per month depending on dose and provider, though those figures vary and should be verified at the point of order. This page on why Wegovy tends to be cheaper walks through the reasons in plain terms.

At nume, we publish transparent pricing on our treatment page rather than printing it in articles, because prices can change and we'd rather you see the current figure than a number that might be out of date. What doesn't change: one price covers the consultation, the prescription, the medicine and free next-working-day delivery. No add-ons, no subscription. The relevant question for a prescription medicine is rarely which option costs least; it is which one a prescriber considers appropriate for you and whether the service supplying it is one you can verify. You can check any online pharmacy, including ours, on the GPhC register, our registration number is 9012878.

If you are weighing both options, a full Wegovy vs Mounjaro comparison and the Mounjaro or semaglutide page cover specific angles in more depth. Which suits you is a clinical decision our prescribers make with you, not one that can be settled by a comparison article.