Is semaglutide as good as tirzepatide for weight loss?

Step 1, understand what each medicine actually does

Semaglutide (sold as Wegovy for weight management) acts on a single gut-hormone pathway: GLP-1 receptors in the brain and digestive system that regulate appetite and slow how quickly the stomach empties. It is made by Novo Nordisk and licensed in the UK for adults with a BMI of 30 or above, or 27 or above alongside a weight-related health condition. The NHS patient information on semaglutide covers what to expect from treatment in plain language.

Tirzepatide (Mounjaro, made by Eli Lilly) targets two pathways simultaneously, GLP-1 and GIP receptors. It is the only dual-agonist weight-loss medicine currently licensed in the UK. Activating both receptor types appears to produce a larger appetite-suppressing and metabolic effect than a single pathway alone, and if you are wondering whether Wegovy is as strong as Mounjaro, that difference in mechanism is a good place to start. You can read more about how the two medicines differ mechanistically on the is tirzepatide the same as semaglutide page.

If you have come across the name Ozempic and are wondering where it fits: Ozempic is also semaglutide, but it is licensed for type 2 diabetes in the UK, not for weight management. Prescribing it for weight loss would be off-label, and it is not something a regulated weight-loss service should offer for that purpose.

Step 2, look at what the trials actually found

This is where the comparison sharpens. The SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks, no diabetes) found that tirzepatide at its highest dose produced an average body-weight reduction of around 20–21%, with some analyses reaching 22.5%. The full SURMOUNT-1 paper in the New England Journal of Medicine sets out the methodology. STEP 1, the equivalent semaglutide trial, reported around 15% average weight loss over 68 weeks at 2.4 mg.

Those are not directly comparable numbers (different trial lengths, different populations) but a head-to-head trial answered the question properly. SURMOUNT-5 (751 adults with obesity and without diabetes, 72 weeks, open-label) ran tirzepatide directly against semaglutide 2.4 mg and found tirzepatide produced statistically greater average weight reduction. NICE's committee discussion of tirzepatide in TA1026 notes that indirect comparisons also favour tirzepatide. It is worth knowing that Wegovy 7.2 mg (a higher maintenance dose approved by the MHRA in early 2026) narrows that gap, reporting around 20.7% average loss over 72 weeks in trials, approaching tirzepatide's highest-dose results.

One clean summary of the key numbers:

Numbers from SURMOUNT-1 (NEJM), STEP 1 (NEJM), and SURMOUNT-5 (NEJM, 2025); NICE TA1026.

Step 3, weigh the practical differences that matter to you

If you are trying to decide between the two, the trial results are only part of the picture. Side effects follow a similar pattern for both medicines, nausea, loose stools, and constipation are the most commonly reported, usually most pronounced after starting or after a dose step, and often settling within a couple of weeks. Neither medicine is dramatically more or less tolerable than the other at a population level, though individual responses vary considerably.

There are a couple of differences worth knowing about. Women taking an oral contraceptive pill alongside tirzepatide are advised to use an additional 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 caution does not currently apply to semaglutide. It is also important to understand that mixing Wegovy and Mounjaro is not something that should be attempted, as taking both medicines together is not supported by the evidence and carries real risks. NHS England's guidance on weight-management injections covers this and similar practical considerations clearly.

If you have previously tried semaglutide without reaching your weight goals, switching is something prescribers do consider. The tirzepatide after semaglutide page looks at that question specifically. And if cost is part of your thinking, the Wegovy vs Mounjaro cost comparison sets out the pricing context honestly.

It is understandable to feel a bit lost when two medicines look similar on the surface but diverge in the evidence. Most people in this position just want someone to cut through it. That is exactly what the consultation is for.

Which one is right for you?

The evidence gives tirzepatide an edge on average weight loss, but average results are not your results. Tolerability, your medical history, any medicines you already take, and which direction your prescriber thinks makes sense for you all matter more than a percentage figure. There is no universal answer a webpage can give you, that is genuinely a clinical decision.

Both semaglutide and tirzepatide are prescription-only medicines under UK law, and a prescriber who has reviewed your full picture decides suitability. At nume, every consultation is read the same day by a GPhC-registered Independent Prescriber. There is no algorithm making that call. If you want to explore semaglutide or tirzepatide with a clinician rather than a webpage, starting a free consultation is the place to begin. Our clinical team can also walk you through anything you are unsure about.