Wegovy or Mounjaro: which is better for weight loss?

SURMOUNT-5: the head-to-head data explained

The SURMOUNT-5 trial randomised 751 adults with obesity (no diabetes) to either tirzepatide or semaglutide 2.4mg for 72 weeks. Tirzepatide produced greater average body-weight reduction, NICE's committee notes this in its discussion of Technology Appraisal TA1026, which recommends tirzepatide for NHS use. The trial is the only large-scale, randomised, head-to-head comparison of these two medicines published to date, and it is the reason most clinical commentary currently positions Mounjaro ahead on average weight loss.

But a few things that trial cannot tell you: it used semaglutide at 2.4mg, which was the standard maintenance dose at the time. The MHRA has since approved a 7.2mg semaglutide dose (Wegovy), and trials of that higher dose reported around 20.7% average weight loss over 72 weeks, narrowing the gap considerably. If you want to dig into whether Mounjaro is genuinely better than Wegovy once that newer dose data is factored in, that question gets a thorough answer on its own page. It also cannot predict what your response will be. Trial averages describe populations, not individuals.

For a fuller look at the numbers side by side, the Wegovy vs Mounjaro comparison on this site breaks down the mechanism, dose schedules and trial figures in more detail.

How the two medicines differ in the body

Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, it activates two gut-hormone pathways involved in appetite regulation and blood-sugar control. Wegovy (semaglutide) works on the GLP-1 pathway alone. That mechanistic difference is one proposed reason for the greater average weight loss seen with tirzepatide; the GIP receptor adds a second signal that appears to amplify the appetite-suppression effect.

Practically speaking, both are once-weekly subcutaneous injections. Both start at a low dose and are titrated upward by a prescriber over several months. The side-effect profiles overlap significantly: nausea, constipation, diarrhoea and indigestion are common with both, typically most noticeable after starting or after a dose increase, and usually settling within days to a couple of weeks. The NHS tirzepatide page and NHS semaglutide page carry patient-level detail on side effects for each.

One practical difference worth knowing: women on oral contraceptives starting Mounjaro should add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because gastric slowing may reduce pill absorption. NHS guidance does not flag the same concern for semaglutide. If you are also considering HRT, that is worth raising at consultation, it affects which route of administration is preferable. If you are already on Wegovy and wondering about switching to Mounjaro, that page covers what the transition involves clinically.

Eligibility, licensing and the NHS picture

Both medicines share the same private licensed eligibility criteria: adults with a BMI of 30 or above, or 27 or above with 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. A prescriber assesses the full picture, BMI alone does not guarantee approval for either medicine.

On the NHS, the two sit under different NICE appraisals and access routes. Tirzepatide (TA1026) is being rolled out in phases through primary care from 2025; semaglutide/Wegovy (TA875) is commissioned via specialist weight management services with a maximum two-year treatment period and waiting lists that are commonly long. Private treatment through a regulated online pharmacy bypasses those waiting lists, subject to clinical suitability. You can verify any online pharmacy on the GPhC register before committing.

On cost, Eli Lilly's UK list price increase in September 2025 pushed Mounjaro's higher-dose pen to around £330, and typical private prices for both medicines range roughly £149–£375 per month depending on dose and provider. The cost comparison page covers this in more detail, including what different headline prices often exclude.

A comparison at a glance

Note: Ozempic is also semaglutide but is licensed for type 2 diabetes management, not weight loss. It should not be used for weight management, a point covered in more depth on the Mounjaro vs Ozempic page. Similarly, Saxenda (liraglutide) is a separate GLP-1 medicine; the three-way comparison sets out how all three sit relative to each other.

Which of these two medicines suits you is a clinical decision our prescribers make with you, based on your health history, current medications, BMI and what matters to you practically. If you are ready to find out, start your free consultation and a prescriber will review your answers the same day. One more practical note: if you are planning around a monthly routine, orders placed by 12pm on any working day go out that afternoon, payday orders, Monday morning starts, all covered.