Which Weight Loss Injection Is Best? UK Options Compared (October 2026)

01 · The core answer

Which weight loss injection is best?

No licensed injection is best for everyone; a prescriber decides what suits you after reviewing your health and current medicines. In the SURMOUNT-1 trial, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone. ² These are trial averages, and individual results vary.

In SURMOUNT-5, the first large head-to-head trial, adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy). Both are effective, licensed treatments; which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone. Wegovy has a dose ladder of 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg, stepping up after 4 weeks on each of 0.25mg, 0.5mg, 1mg and 1.7mg, so the 2.4mg maintenance dose starts from week 17.¹⁸ Our guide to weight loss injections goes deeper on each one.

02 · Side by side

Weight loss injections compared

03 · Your decision

What should you do next?

Start by asking whether you meet the licensed criteria, then compare running costs. Our monthly cost breakdown shows what each month looks like. A 2.5mg Mounjaro pen has a standard price of £169.99, and the Mounjaro pen page has live prices for every dose. If you are ready, our weight loss clinic starts with a free consultation.

Related guide: Best Weight Loss Medication UK Discount Code.

04 · How Mounjaro works

How Mounjaro works compared with other injections

Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ Most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.

This dual action distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic). Whether that difference matters for you is a prescriber's judgement, not a rule.

05 · Realistic expectations

Realistic expectations on any injection

Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest; most measurable progress builds from 5mg onward, month by month. Trials measured results at 72 weeks, so think in months, not days.²

Treatment is always used alongside a reduced-calorie diet and increased physical activity. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.

06 · Safety and interactions

Safety, interactions and who should ask first

Because Mounjaro slows stomach emptying, it can affect how quickly some oral medicines are absorbed, particularly when you start treatment or increase the dose. Tell your prescriber about everything you take, especially warfarin or other narrow-margin medicines, insulin, or sulfonylureas, where doses may need reducing to avoid low blood sugar.¹

Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle. Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. Report any suspected side effect through the Yellow Card scheme.¹⁹

07 · NHS or private

NHS or private supply

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first.⁴ Many people who meet the licensed criteria choose regulated private treatment rather than wait.

Compare providers before buying; our price guide explains how, and our weight loss medication injection overview covers the wider picture. Only buy from a GPhC-registered pharmacy; ours is GPhC 9012878.