Tirzepatide vs Semaglutide: Weight Loss Comparison

Step 1: Understand what each medicine actually does

Semaglutide (the active ingredient in Wegovy) mimics the GLP-1 hormone, slowing gastric emptying and reducing appetite signals in the brain. It has been available in the UK for weight management since 2021 and has a well-established safety profile built on the STEP trial programme. The STEP 1 trial, published in the New England Journal of Medicine, reported an average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose.

Tirzepatide (Mounjaro) adds a second pathway: it activates both GIP and GLP-1 receptors. That dual action appears to produce a stronger effect on appetite and fat metabolism in most people. SURMOUNT-1 reported average weight reductions of around 20–21% at the highest 15mg dose over 72 weeks, with some analyses reaching roughly 22.5%. It is the only dual-agonist weight-loss medicine currently licensed in the UK. If you are weighing up which of the two options is likely to work harder for you, our guide to tirzepatide vs semaglutide for weight loss walks through the evidence in plain terms. The NHS medicines page for tirzepatide gives a patient-level overview of how it works and what to expect.

Neither medicine is a fast fix. Both work alongside a reduced-calorie diet and increased physical activity, and both require consistent use across several months to reach their licensed maintenance doses.

Step 2: Read the head-to-head trial data

Until 2025, direct comparisons relied on indirect analyses, useful, but limited. The SURMOUNT-5 trial changed that. In this open-label trial involving 751 adults with obesity but without diabetes, participants were randomised to tirzepatide or semaglutide 2.4mg over 72 weeks. Tirzepatide produced greater average weight reduction. NICE's appraisal of tirzepatide (TA1026) also noted that indirect comparisons from the evidence review favoured tirzepatide over semaglutide for weight loss. If you want to dig into the raw numbers, including the comparison in kilograms lost rather than percentage, our page on the kilogram-weight difference covers that in detail.

There is an important nuance. Wegovy now has a 7.2mg dose, approved by the MHRA in January 2026 and available in a dedicated single-dose pen from April 2026. Trials at that higher dose reported around 20.7% average weight loss over 72 weeks, which narrows the gap with tirzepatide 15mg considerably. Dose availability should always be confirmed at your consultation. For a fuller breakdown of how the two brands sit against each other, the Mounjaro vs Wegovy comparison covers the licensing, dosing schedules and practical differences side by side.

A note on products that sometimes appear in searches: Ozempic is also semaglutide, but it is licensed in the UK for type 2 diabetes, not weight loss. Rybelsus is oral semaglutide licensed for diabetes. Neither should be used for weight management. The Mounjaro vs Ozempic page explains the distinction clearly.

Step 3: Consider what differs in daily use

Both medicines are injected once a week, and injection day is something patients quickly build into their routine, many keep the pen in the fridge door so the weekly reminder takes care of itself. Tirzepatide's KwikPen delivers four doses from a single pen; each pen lasts a month. Wegovy uses individual pre-filled pens. Wegovy also now exists as a daily oral tablet (25mg maintenance), which suits people who prefer not to inject at all, though the tablet has specific morning-routine requirements around timing and food that not everyone finds convenient.

Side effects follow a broadly similar profile for both: nausea, constipation, diarrhoea, indigestion and fatigue are the most commonly reported, typically most noticeable around a dose increase and settling within one to two weeks for most people. Storage for both injection forms requires refrigeration between 2°C and 8°C; always check the Patient Information Leaflet for the exact room-temperature window permitted during travel or use. The detailed tirzepatide vs semaglutide overview covers side effects, contraindications and the contraception considerations that apply specifically to tirzepatide.

On cost, the two medicines sit broadly in the same private-market range, though prices vary by dose and provider. Our cost comparison page sets out what typical UK private prices look like and what a legitimate quoted price should include.

Step 4: How a prescriber decides which is right for you

Trial averages are population-level figures. Your starting weight, any existing conditions, medicines you already take, and how your body responds to GLP-1 or GIP stimulation all shape the clinical picture. NICE's thresholds for NHS access differ slightly between the two medicines, and both carry ethnic-background BMI adjustments of 2.5 kg/m² under UK guidance. Lower thresholds can apply for South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds, eligibility pages on our weight loss treatment overview explain those criteria in full.

At nume, a GPhC-registered Independent Prescriber reads your consultation answers the same day. They look at your full picture, not just which medicine produced a larger number in a trial. The consultation is free, there is no subscription, and if treatment is approved you receive it the following working day. A prescriber reviewing your case with you is the only reliable way to answer the tirzepatide vs semaglutide question for you specifically. You can explore both options and ask questions through our consultation page.