Tirzepatide and Semaglutide Head to Head: Which One Fits Your Situation?

What you're actually deciding between

The decision most people reach this page with is simple on the surface: tirzepatide (sold in the UK as Mounjaro) or semaglutide (sold as Wegovy). Both are once-weekly subcutaneous injections, both work by slowing gastric emptying and reducing appetite, and both are licensed for weight management in adults with a BMI of 30 or above, or 27 or above alongside a weight-related condition such as high blood pressure or type 2 diabetes.

The mechanism is where they diverge. Semaglutide activates a single pathway: the GLP-1 receptor. Tirzepatide activates two (GLP-1 and GIP) making it the only dual-agonist weight-loss medicine currently licensed in the UK. Whether that extra pathway translates into a meaningful difference for any individual person is precisely what the head-to-head trial set out to test. You can read more about the underlying pharmacology on our page on whether tirzepatide and semaglutide are the same medicine.

One thing worth stating plainly: if you're uncertain whether Ozempic is tirzepatide or semaglutide, it is semaglutide, but it is licensed for type 2 diabetes, not weight loss. If someone's suggesting Ozempic for weight management, that is the wrong product. The relevant licensed options are Mounjaro and Wegovy.

What the SURMOUNT-5 trial actually found

The SURMOUNT-5 trial (published in the New England Journal of Medicine in 2025) was a 72-week, open-label study of 751 adults with obesity but without diabetes. It compared tirzepatide at its maximum tolerated dose against semaglutide 2.4mg. Tirzepatide produced statistically significantly greater average weight loss. The NICE technology appraisal for tirzepatide (TA1026) also notes that indirect comparisons favour tirzepatide, though it flags the usual caveats about cross-trial populations.

Semaglutide's STEP 1 trial (2.4mg, 68 weeks) reported an average body-weight reduction of around 15%. SURMOUNT-1 reported around 20–21% at tirzepatide 15mg. Neither figure is a prediction for what you will lose, they are averages across large groups of people, and individual responses vary considerably. What matters clinically is how you respond over your first months of treatment.

The comparison table below summarises the key clinical facts side by side.

One nuance the table can't carry: the MHRA approved a 7.2mg maintenance dose of semaglutide in January 2026, with a dedicated single-dose pen following in April 2026. Trial data at 7.2mg reported around 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide 15mg considerably. The landscape is still shifting, which is part of why the question of whether semaglutide matches tirzepatide doesn't have a static answer.

The factors that tip a prescriber's decision

Trial averages are useful context, but they are rarely the deciding factor in a clinical consultation. A prescriber considering these two medicines will think about your full medical picture: what conditions you're managing, what other medicines you take, how you've responded to any previous treatment, and what your preferences are around injections versus tablets.

The oral Wegovy tablet (approved in the UK in June 2026 as the first oral GLP-1 licensed here for weight management) changes the conversation for people who are needle-averse or whose lifestyle makes refrigerated storage difficult. It is taken first thing in the morning on an empty stomach, before food or coffee; no fridge required. For someone who travels frequently, that alone can be a meaningful practical advantage.

Contraception is also a consideration. Our guide to choosing between semaglutide and tirzepatide covers this in more detail, but the short version is that women taking oral contraceptives should add a barrier method for the first four weeks of tirzepatide and for four weeks after each dose increase, because absorption of the pill may be affected. NHS guidance does not flag the same requirement for semaglutide.

Previous treatment matters too. If you've already tried semaglutide and found the results insufficient, the question shifts, and our page on moving to tirzepatide after semaglutide addresses what that transition looks like clinically.

What none of this tells you, and how to find out

A comparison page can set out the evidence honestly. It cannot tell you which medicine your prescriber will consider appropriate for you, because that depends on information only a clinical assessment can surface. No comparison of trial averages substitutes for that conversation. Some people are not suitable for either, there are contraindications, conditions that require extra care, and medicines that interact in ways that need weighing up.

Our prescribers review every consultation the same day. A clinician (not an algorithm) reads your answers and makes the call. If you're unsure which direction the conversation will go, it helps to know that suitability questions are exactly what the consultation is for. You can also read about our weight-loss treatment options more broadly, or take a look at the Wegovy versus Mounjaro comparison if brand-level details are useful. Both routes start in the same place.

Speak to our prescribers, start your free consultation here.