About Mounjaro: the evidence behind the medicine

How tirzepatide differs from other weight-loss medicines

Tirzepatide's defining feature is that it binds to receptors for two hormones: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Both are released naturally in the gut after eating. Activating them together slows the rate at which the stomach empties, increases feelings of fullness after meals, and reduces the drive to eat between them. The result is a sustained reduction in overall calorie intake without requiring the kind of conscious restraint that most conventional diets demand.

This dual-receptor action is what separates Mounjaro from semaglutide-based treatments, which target GLP-1 alone. The distinction matters clinically, and the full pharmacology of tirzepatide is worth understanding if you want to know why that difference produces different results in trials. It also matters for side-effect conversations, because the GIP pathway may contribute to the tolerability profile some people report.

One misconception worth addressing: some people assume Mounjaro is a stimulant or appetite suppressant of the old central-nervous-system kind. It is neither. It works through hormonal signalling, not by speeding up your heart rate or overriding your brain with stimulant chemistry. The NHS medicine page for tirzepatide explains the mechanism clearly if you want a patient-facing account from a source independent of any pharmacy.

What SURMOUNT-1 actually found — and what it means

The pivotal evidence for Mounjaro in weight management comes from the SURMOUNT programme. SURMOUNT-1 randomised 2,539 adults with obesity or overweight plus at least one weight-related condition over 72 weeks. Participants at the 15 mg maintenance dose lost an average of around 20–21% of their body weight; some analyses put the figure closer to 22.5%. Those are averages across the trial population, individual results varied, as they always do, and the medicine works alongside a reduced-calorie diet and increased physical activity, not instead of them.

NICE reviewed this and the wider SURMOUNT data before issuing its recommendation in TA1026 in December 2024. The recommendations chapter of NICE TA1026 sets out the eligibility criteria in detail, including the body-mass-index thresholds and the weight-related conditions that must be present. Lower BMI thresholds apply for people from certain ethnic backgrounds under that guidance.

A head-to-head comparison matters here too. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found tirzepatide produced greater average weight reduction than semaglutide 2.4 mg over 72 weeks in adults with obesity who did not have diabetes. That is direct evidence, not a modelled comparison. For a closer look at how the two medicines sit alongside each other, the tirzepatide overview covers the comparison in more depth.

Who Mounjaro is licensed for, and how prescribers assess it

The UK licence covers adults with a BMI of 30 or above, or a BMI from 27 upward where at least one weight-related condition is present, for example, high blood pressure, type 2 diabetes, high cholesterol, obstructive sleep apnoea, or cardiovascular disease. BMI alone does not determine suitability; a prescriber reviews the full clinical picture, including other medicines you take, your medical history and whether any contraindications apply.

Mounjaro carries a Black Triangle (▼) designation from the MHRA, meaning it is subject to additional monitoring while post-market safety data accumulates. That is standard for newer medicines in the UK and does not reflect a specific safety concern, but it does mean reporting any unexpected side effects via the MHRA Yellow Card scheme is actively encouraged.

Pregnancy, breastfeeding and planning a conception are clear contraindications, the medicine is not recommended in any of those situations, and under-18s are outside the licensed age group. Women using oral contraceptives should discuss the interaction with their prescriber, because tirzepatide's effect on gastric emptying can reduce pill absorption during the first weeks of treatment and after each dose increase.

If you are thinking about what treatment might cost, the Mounjaro price comparison guide gives an honest account of how private pricing works and what a legitimate service includes.

Getting Mounjaro on the NHS versus through a regulated private pharmacy

NHS access to tirzepatide is being rolled out in phases. From June 2025, patients with a BMI of 40 or above and four or more of a defined list of weight-related conditions became eligible; a second cohort at BMI 35–39.9 opened in June 2026. GP practices may prescribe it under the 2026/27 QOF contract, though participation is voluntary, so availability varies. Every NHS patient also takes part in wraparound dietary and activity support as part of the programme.

For people who do not meet those criteria yet, or who prefer not to wait, a regulated private pharmacy is the alternative legal route. At nume, every application is read by a GPhC-registered Independent Prescriber (a real clinician, not automated decision-making) on the day it arrives. Identity and weight are verified, and treatment is only dispatched once it has been clinically approved. You can confirm our pharmacy's registration directly on the GPhC register.

For context on what to expect from the process, the Mounjaro treatment page sets out how a private consultation works and what happens at each stage, and if you want a thorough grounding before you begin, our guide covering all about Mounjaro brings together everything from how the medicine works to what to expect week by week. If you have specific questions before starting, our FAQ page covers the questions prescribers hear most often, including queries about supplements, and there is a dedicated page on taking inositol alongside Mounjaro for anyone exploring that combination. When you are ready, you can speak to our prescribers through a free consultation with no obligation.