Mounjaro information: what the clinical evidence shows

What the SURMOUNT trials established about tirzepatide

The most rigorous evidence for Mounjaro comes from the SURMOUNT clinical programme, involving thousands of adults across multiple trials. SURMOUNT-1, published in the New England Journal of Medicine, randomised 2,539 adults with obesity but without type 2 diabetes and followed them for 72 weeks. At the 15 mg maintenance dose, participants lost an average of around 20–21% of their starting body weight — a figure that had not been reached by any previously licensed weight-loss medicine. Roughly 90% of participants at that dose achieved at least 5% weight loss, and more than a third lost 25% or more.

A later head-to-head study, SURMOUNT-5, compared tirzepatide directly with semaglutide 2.4 mg and found tirzepatide produced greater average weight loss over 72 weeks. That comparison matters for anyone weighing up their options; you can read more about the individual tirzepatide information on our tirzepatide overview page.

These figures are trial averages. Real-world results vary with adherence, diet, activity level, and individual biology. No medicine produces identical outcomes for every person, and a prescriber will always discuss realistic expectations during your consultation.

How Mounjaro's dual mechanism differs from other GLP-1 medicines

Most injectable weight-loss medicines on the UK market target a single receptor: GLP-1, which slows gastric emptying and reduces appetite by signalling fullness to the brain. Tirzepatide adds activation of the GIP receptor on top of that. GIP (glucose-dependent insulinotropic polypeptide) is released from the gut after eating and plays a role in fat storage, energy balance, and insulin response. Acting on both pathways simultaneously appears to produce a stronger and more sustained appetite-reduction effect than GLP-1 activation alone, which is the likely mechanism behind the larger trial results.

A question our prescribers hear most weeks is whether the dual mechanism means more side effects. The short answer is that the side-effect profile is broadly similar to other GLP-1 medicines: predominantly gastrointestinal symptoms such as nausea, constipation, and diarrhoea, most noticeable at the start of treatment or after a dose increase, and generally settling over days to a couple of weeks. The NHS medicines page for tirzepatide lists the full side-effect profile clearly, and our Mounjaro information leaflet page covers what to watch for in plain language.

Storage follows the same refrigerated principle as other injectables: 2–8°C until opened. For the exact room-temperature window and other handling details, our tirzepatide information sheet covers the key handling and storage guidance in one place.

Who Mounjaro is licensed for, and what NICE recommends for NHS access

The UK product licence covers adults with a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition, for example, high blood pressure, high cholesterol, obstructive sleep apnoea, prediabetes or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance, reflecting differences in metabolic risk at lower body weights.

NICE's appraisal TA1026 set more specific criteria for NHS use: a BMI of 35 or above plus at least one weight-related comorbidity from a defined list, with the same ethnic-background adjustments. The NHS is rolling out access in phased cohorts, the most recent phase, which activated in June 2026, extended eligibility to people with a BMI of 35 to 39.9 alongside four or more qualifying conditions. Not everyone who meets the licence criteria will qualify under current NHS commissioning rules, and many people choose private treatment in the meantime. Our Mounjaro treatment page explains both routes in detail, and our prescribing information page covers what a prescriber looks at when assessing suitability.

BMI alone is never the whole picture. A prescriber considers your full health history, current medicines, and any contraindications (including a personal or family history of certain thyroid conditions) before any prescription is issued. Mounjaro is not licensed for use in pregnancy, during breastfeeding, or in people under 18; these are firm boundaries, not suggestions.

Cost context, and the right questions to ask any provider

Private Mounjaro pricing varies significantly between providers and across doses. Since Eli Lilly raised UK list prices in September 2025, typical private market prices range from roughly £149 to £375 per month depending on dose and clinic. That spread reflects genuine differences in what is included: some headline prices cover only the medicine, with consultation fees, prescription charges, and delivery billed separately. If you want to understand how the numbers compare, our Mounjaro price comparison page breaks this down honestly.

At nume, one price covers the consultation, the prescription, the medicine, and free next-working-day delivery. There are no subscription traps and no auto-renewals; every repeat order goes through a fresh clinical review. We are not the cheapest option on the market, and we are straightforward about that. What you are paying for is a GPhC-registered pharmacy, a same-day clinical review by a real prescriber, and aftercare available seven days a week.

If you have questions about anything above (or want to understand whether Mounjaro might suit your situation) our free consultation is the right next step. A prescriber will read your answers the same day and give you a clear, honest assessment. There is no obligation to proceed.