Mounjaro Drug vs Wegovy: Choosing Between the Two Leading Weight-Loss Injections

The decision most people are actually trying to make

A question our prescribers hear most weeks runs something like: "I've heard Mounjaro is stronger, so why would anyone choose Wegovy?" It's the right question, and the honest answer is that "stronger on average in a trial" and "right for this person" are different things. Both medicines slow gastric emptying, reduce appetite and are taken as once-weekly subcutaneous injections. Their mechanisms diverge at the receptor level: tirzepatide binds both the GIP and GLP-1 receptors, making it the only dual-agonist weight-loss medicine licensed in the UK. Semaglutide works on GLP-1 alone. Whether that mechanistic difference matters for you specifically depends on your health background, any medicines you already take, and what your prescriber finds when they review your case.

The comparison below covers the facts most relevant to this decision, not a ranking, but a structured look at where the medicines differ. For a deeper dive into how the trial data shapes the choice, the clinical case for each medicine covers the nuances the headline numbers miss.

What the clinical evidence actually shows

The SURMOUNT-1 trial (72 weeks, adults with obesity, no diabetes) reported average body-weight reductions of around 20–21% at tirzepatide's 15mg dose, with some analyses reaching approximately 22.5%; the NEJM paper from the STEP 1 trial reported around 15% average loss with semaglutide 2.4mg over 68 weeks. In SURMOUNT-5, a direct head-to-head published in the New England Journal of Medicine in 2025, tirzepatide produced greater average weight reduction than semaglutide 2.4mg across 72 weeks in 751 adults with obesity and no diabetes. NICE's appraisal of tirzepatide noted that indirect comparisons favour tirzepatide, though it acknowledged the evidence base continues to develop.

A newer semaglutide picture exists, too. The MHRA approved a 7.2mg Wegovy dose in January 2026 and a dedicated single-dose 7.2mg pen in April 2026, with trial data reporting around 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide's highest dose considerably. NICE has appraised both: Wegovy (TA875) and Mounjaro (TA1026) each carry formal recommendations, with differing NHS criteria. You can read the published NICE recommendation for tirzepatide directly at NICE TA1026.

The weight-loss results comparison goes further into how to read these figures alongside each other.

Where the medicines differ beyond average weight loss

Side-effect profiles overlap substantially. Nausea, constipation, diarrhoea and indigestion appear across both, most commonly after starting or moving to a higher dose, and usually settle within one to two weeks. The NHS medicines pages for tirzepatide and semaglutide each list the full side-effect profiles and when to seek medical help, worth reading before you start either.

One practical difference matters for women using oral contraceptives: for tirzepatide specifically, UK guidance advises adding a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption may be reduced. The same requirement does not currently apply to semaglutide. If you are weighing up how tirzepatide and semaglutide compare as treatments, this contraceptive difference is one of the more clinically meaningful practical distinctions to discuss at consultation. If HRT is part of your health picture, the same principle applies to oral HRT on tirzepatide, a conversation worth having at consultation.

The titration schedules also differ in granularity. Mounjaro starts at 2.5mg; the first pen's job is to settle your system, not yet to treat. Wegovy begins at 0.25mg. Both move through a stepped schedule the prescriber manages. Neither medicine's dose timing or step-up should be adjusted without clinical guidance. The practical differences between the two covers injection technique, storage and switching in more depth.

The cost and access picture

On the NHS, tirzepatide access is phased by cohort and requires meeting strict BMI and comorbidity criteria; Wegovy is available through specialist weight management services under TA875, subject to waiting lists that vary considerably by area. For many people, neither is currently accessible through the NHS without a wait. Private treatment through a regulated online pharmacy is the alternative, and if you are still deciding between the two options, our Mounjaro vs Wegovy guide walks through the considerations that are most relevant when making that choice privately. For a prescription medicine, a small saving is the wrong test; what matters is clinical oversight, a genuine supply chain and a pharmacy you can verify. The MHRA has issued clear warnings about fake weight-loss pens sold without any clinical assessment online, counterfeit tirzepatide manufacturing sites have been raided in the UK. Any regulated pharmacy can be checked on the GPhC register.

The weight-loss treatment overview summarises what private treatment with nume includes at a single transparent price. If you want to explore both medicines with a prescriber and see which one fits your situation, the place to start is a free consultation.