Tirzepatide vs Semaglutide: What the Evidence Actually Shows

You've read that one is 'stronger' — here's what that claim is actually based on

The comparison most people are searching for comes from SURMOUNT-5, a 72-week open-label trial that put tirzepatide (up to 15mg) directly against semaglutide 2.4mg in adults with obesity but without type 2 diabetes. Tirzepatide produced greater average weight reduction. That trial, published in the New England Journal of Medicine, is the closest thing to a definitive head-to-head the field has. It is also cited in NICE's appraisal of tirzepatide (TA1026), which notes that indirect comparisons consistently favour tirzepatide at its higher doses.

A practical thing worth knowing: semaglutide's standard maintenance dose was 2.4mg weekly, but the MHRA approved a higher 7.2mg maintenance dose in early 2026, with a dedicated single-dose pen confirmed in April 2026. Trial data at 7.2mg reported around 20.7% average weight loss over 72 weeks, which closes the gap with tirzepatide's 15mg results considerably. If you want a deeper look at how tirzepatide and semaglutide compare for weight loss across doses and mechanisms, it's worth asking which semaglutide dose is being discussed, because the picture has shifted.

You can do a quick sense-check in under a minute: look up the pharmacy or clinic you're considering on the GPhC pharmacy register to confirm they're authorised to dispense prescription medicines before reading any results claims they publish. Legitimate services are verifiable.

Neither medicine is a guaranteed outcome. Both work alongside a reduced-calorie diet and increased physical activity; neither is licensed for cosmetic use.

Where the two medicines sit on eligibility and who can access them

On paper, the licensed eligibility criteria are similar: both are approved for adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related health condition such as high blood pressure, high cholesterol, obstructive sleep apnoea or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone is never the whole picture; a prescriber weighs your full health history before recommending either treatment.

The NHS routes differ. NICE's recommendation for tirzepatide (TA1026) covers patients with a BMI of 35 or above plus at least one qualifying comorbidity; the phased NHS rollout began in June 2025 and is expanding. NICE's recommendation for semaglutide (TA875) similarly requires a BMI of 35 or above but adds a two-year maximum treatment duration and the requirement for a specialist multidisciplinary weight management service. Both have waiting lists. If you're exploring whether to switch or which to try first, our page on switching between the two covers the clinical considerations in more detail.

Privately, both medicines are available through regulated online pharmacies subject to a full clinical assessment. Our prescribers at nume review both options with you.

Side effects: broadly similar profiles with some meaningful differences

Both medicines share the same dominant side-effect category: gastrointestinal. Nausea is the most commonly reported effect, particularly after starting or increasing the dose. Vomiting, loose stools, constipation, reflux and fatigue are also reported with both. These effects tend to ease within days to a couple of weeks for most people as the body adjusts. The titration schedule (starting low and stepping up gradually) exists specifically to reduce this burden.

One clinically relevant distinction involves oral contraceptives. For tirzepatide, the MHRA advises adding a non-oral method of contraception (such as condoms) during the first four weeks of treatment and for four weeks after any dose increase, because slowed gastric emptying may reduce how much of the pill is absorbed. The same precaution does not have equivalent published evidence for semaglutide, though the NHS recommends discussing contraception with your prescriber before starting either medicine. You'll find full guidance on this in the NHS England advice on weight-management injections.

Pancreatitis is a rare but serious risk with GLP-1 medicines generally: severe, persistent stomach pain (especially if it spreads to the back) warrants urgent medical attention. Both medicines carry a Black Triangle (▼) status, meaning the MHRA collects additional safety data on an ongoing basis. Patients can report suspected side effects at any time via the Yellow Card scheme.

Which one is right for you, and how to find out

The honest answer is that neither trial data nor this page can tell you. The SURMOUNT-5 results are a group average; individual responses to both medicines vary, and factors like your medical history, current medications, how you prefer to take treatment (injection versus, now, tablet) and whether you've tried one before all shape the clinical picture. If you've already been on semaglutide and want to know whether tirzepatide might be the next step, that's a conversation for a prescriber, not a search engine. Our detailed look at whether tirzepatide outperforms semaglutide goes further on the trial evidence if you want more before that conversation.

One note on products that sometimes appear in this comparison: Ozempic is also semaglutide, but it is licensed for type 2 diabetes, not weight loss. Rybelsus is oral semaglutide at diabetes doses (3mg, 7mg, 14mg) and similarly is not a weight-loss medicine. The weight-loss oral option is Wegovy tablets, approved by the MHRA in June 2026. For a side-by-side of how semaglutides and tirzepatide differ in mechanism, dosing and outcomes, our Mounjaro vs Wegovy comparison page runs through the practical differences, including how the two stack up on cost, dosing and availability. And if cost is part of your decision, what Wegovy costs compared to Mounjaro covers the pricing context without the noise.

A prescriber at nume (sorry, at nume) reviews your consultation the same day it comes in. Which medicine suits you is a clinical decision our prescribers make with you, not a conclusion this page can reach on your behalf. Check your eligibility and start that conversation.