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What is Mounjaro?

About this page. Written by the GLPInfo editorial team with AI assistance from the official sources listed at the end, and approved by the site owner before publication. It has not been reviewed by a named clinician. Published 27 Aug 2026 · last updated 27 Aug 2026 · next scheduled review 27 Nov 2026.

This page is information, not medical advice. It never tells you which medicine, dose or format is right for you: those decisions sit with you and a qualified prescriber. Spotted an error? Tell us and we'll fix it fast.

Mounjaro is the brand name for tirzepatide, a once-weekly injection made by Eli Lilly that is licensed in the UK for weight management alongside diet and physical activity. It is the first medicine of its kind to act on two gut-hormone receptors at once.

How it works

Tirzepatide is a dual receptor agonist: it activates both the GLP-1 receptor and the GIP receptor, two gut-hormone pathways involved in appetite and blood-sugar regulation. In plain terms it reduces appetite, slows how quickly the stomach empties, and helps the body respond to food with less hunger. It is a prescription-only medicine, taken as a once-weekly injection with a pre-filled KwikPen that contains four weekly doses.

Licence and doses

Mounjaro is MHRA-licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 and above with at least one weight-related condition, alongside a reduced-calorie diet and increased physical activity. Treatment starts at 2.5mg weekly and is increased gradually by the prescriber through 5mg, 7.5mg, 10mg and 12.5mg to a maximum of 15mg, with at least four weeks at each step. The step-ups exist to manage side effects, most commonly gastrointestinal, and not everyone needs the highest dose.

What the trials showed

In SURMOUNT-1 (72 weeks, adults with obesity without diabetes, published in the New England Journal of Medicine in 2022), tirzepatide 15mg produced an average body-weight reduction of about 20.9%, against 3.1% with placebo. In the only direct head-to-head against semaglutide, SURMOUNT-5 (72 weeks, published 2025), average weight loss was 20.2% with tirzepatide versus 13.7% with semaglutide at maximum tolerated doses. Trial averages hide wide individual variation, and trial participants receive structured diet and activity support.

Side effects and safety

The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting and constipation, most often during dose increases. The patient information leaflet lists the full range including the serious but less common risks such as pancreatitis, and your prescriber assesses suitability against your history. Report suspected side effects through the MHRA Yellow Card scheme. See our Mounjaro vs Wegovy comparison for how it compares with semaglutide.

What it costs today: first-month Mounjaro prices at the 2.5mg starting dose currently start from £94 across the 20 UK online providers we compare, checked 27 Aug 2026 and re-checked automatically every 12 hours. Compare all Mounjaro prices or see the true multi-month cost.

Frequently asked questions

Is Mounjaro available on the NHS?

Partly. Tirzepatide is being rolled out in primary care in phases under NICE guidance, prioritising people with the highest clinical need. Most people currently using it for weight loss access it privately through regulated online providers. Criteria change; check the NHS website or your GP for the current position.

How much does Mounjaro cost in the UK?

Prices vary widely by provider and dose. Our live comparison of UK online pharmacies shows current first-order and ongoing prices per dose, re-checked every 12 hours: compare Mounjaro prices. The ongoing price matters more than the first-month offer: understanding true cost.

How is Mounjaro different from Wegovy?

Mounjaro (tirzepatide) acts on two hormone receptors, Wegovy (semaglutide) on one. In the SURMOUNT-5 head-to-head trial average weight loss was greater with tirzepatide, but individual responses vary and a prescriber weighs far more than trial averages. Full comparison.

Related: Mounjaro price comparison · cheapest Mounjaro today · true cost guide · how to check a provider

Sources

  1. SURMOUNT-1 trial, tirzepatide for obesity, New England Journal of Medicine (2022)
  2. SURMOUNT-5 head-to-head trial, tirzepatide vs semaglutide, New England Journal of Medicine (2025)
  3. Mounjaro patient information, electronic medicines compendium (emc)
  4. NICE guidance on tirzepatide for managing overweight and obesity