Tirzepatide versus Semaglutide for Weight Loss: What the Evidence Shows

What the trials actually found, and why the SURMOUNT-5 result matters

The clearest picture of how these two medicines stack up comes from the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025. It was the first large randomised head-to-head comparison of tirzepatide (at doses up to 15 mg) and semaglutide 2.4 mg in adults living with obesity but without type 2 diabetes, followed over 72 weeks. If you want a thorough breakdown of what that comparison showed, our page on tirzepatide vs semaglutide for weight loss covers the findings in detail. NICE's committee, in its appraisal of tirzepatide (TA1026), also noted that indirect comparisons favour tirzepatide over semaglutide.

The earlier individual trials reinforce this. SURMOUNT-1 (2,539 adults, 72 weeks) reported average body-weight reductions of roughly 20–21% at the 15 mg dose, with some analyses reaching around 22.5%. The STEP 1 trial for semaglutide 2.4 mg (68 weeks) found an average reduction of approximately 15%. A higher semaglutide dose (7.2 mg, approved by the MHRA in early 2026) has since reported around 20.7% average loss over 72 weeks, which closes the gap with tirzepatide considerably.

These are trial averages. Individual results vary based on starting weight, lifestyle factors, and how well each person tolerates titration. Our prescribers are asked this exact comparison question most weeks, and the honest answer is always the same: the headline percentage is one input, not the whole story.

One clarification worth making: Ozempic is also semaglutide, but it holds a UK licence for type 2 diabetes management, not weight loss. If you have seen Ozempic discussed in a weight-loss context, that use sits outside its licensed indication. The medicine licensed for weight loss is Wegovy. You can read more about how Mounjaro and Ozempic differ if that question has come up for you.

Which patients tend to be considered for each, and what eligibility looks like in practice

Both medicines share a broadly similar licensed population: adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as hypertension, type 2 diabetes, dyslipidaemia, or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance, specifically, a 2.5 kg/m² reduction for South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds.

In practice, the NICE recommendations differ in a way that matters for NHS access. NICE's appraisal of semaglutide (TA875) specifies use within a specialist weight management service, with a maximum treatment duration of two years. The tirzepatide appraisal (TA1026) does not carry the same two-year cap, and NHS commissioning for tirzepatide is currently being phased in through GP practices under a new contract from April 2026, starting with the highest-need patients.

Privately, through a regulated pharmacy, those NICE service restrictions do not apply in the same way, what matters is licensed eligibility and a prescriber's clinical judgement. A detailed look at how Wegovy and Mounjaro compare on eligibility and access covers this in more depth. BMI alone is never the only consideration; the prescriber reviews the whole clinical picture before approving treatment.

Side effects, tolerability, and what day-to-day use looks like

Both medicines share a gastrointestinal side-effect profile rooted in how GLP-1 agonism works: slowing gastric emptying and reducing appetite also tends to produce nausea, loose stools, constipation, bloating, or indigestion, particularly in the weeks after starting or after a dose increase. These effects are generally mild to moderate and ease as the body adjusts. They are not a reason to stop without speaking to your prescriber first.

The NHS's patient information for tirzepatide and for semaglutide covers the full side-effect profiles in detail. One point specific to tirzepatide: because it activates the GIP pathway in addition to GLP-1, women taking oral contraceptives 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, as absorption of the pill may be affected. This is not a documented concern with semaglutide, though all GLP-1 medicines delay gastric emptying to some degree.

On the question of how they feel to use: both are once-weekly subcutaneous injections, stored in the fridge, with pens that most people find straightforward after the first use. Wegovy also now exists in an oral tablet form (the 25 mg Wegovy tablet, approved by the MHRA in June 2026) which some people prefer to injections. That option sits under a separate clinical assessment. If injection anxiety is a factor in your thinking, it is worth raising during your free consultation.

Cost context and the clinical decision that follows

Price is a reasonable question. Since Eli Lilly raised UK list prices in September 2025, private tirzepatide has typically ranged from roughly £149 to £375 per month depending on dose and provider. Semaglutide sits in a similar bracket, and our page on semaglutide vs Mounjaro for weight loss sets out how the two medicines compare on cost alongside clinical outcomes. The full Mounjaro and Wegovy price comparison sets this out honestly.

For a prescription medicine, though, price alone is a poor guide. What matters is that the medicine is genuine, the clinical assessment is thorough, and there is someone to call if you have a question on a Tuesday evening. At nume we are deliberately not competing on headline price. One fee covers the consultation, the prescription, the medicine, next-working-day DPD delivery, and aftercare seven days a week. No subscription, no hidden extras. You can verify our pharmacy on the GPhC register at any time, our registration number is 9012878.

The comparison between tirzepatide and semaglutide is one our prescribers work through with each patient individually, and our guide to semaglutide versus Mounjaro is a useful starting point if you want to read more before your consultation. Which medicine is right for you is a clinical decision, shaped by your BMI, your health history, your other medicines, and how you want to take treatment. That conversation starts with a free consultation, and there is no pressure toward either option before it happens. See how nume works if you want more background before you begin.