GLP-1 and Weight: How These Medicines Work and What to Expect (October 2026)

01 · Decision

Is a GLP-1 medicine relevant to your weight?

It is relevant if you want medical support for weight management alongside a reduced-calorie diet and more physical activity. Mounjaro is licensed for weight management in adults with a BMI of 30 or above, or a BMI between 27 and 30 with at least one weight-related condition. A prescriber looks at your overall health, your weight-related conditions and your other medicines.

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 (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

02 · Next step

What to do next

Start with a free online consultation, reviewed by a GPhC-registered prescriber. If you want to see current options, our GLP-1 weight loss injections page explains how ordering works, and the Mounjaro pen page shows live prices, which start at £169.99 per month at the 2.5mg dose (standard price). Our weight loss clinic covers the wider picture.

03 · How GLP-1 works

How GLP-1 medicines affect appetite

They act on gut-hormone receptors that regulate appetite and digestion. 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

In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet. This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹ Ozempic is semaglutide licensed for type 2 diabetes — it is not a UK weight-loss medicine, and prescribing it privately for weight loss is off-label.

04 · What trials show

What the trials show about weight

The main Mounjaro result comes from SURMOUNT-1. In the SURMOUNT-1 trial of 2,539 adults, 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. These are trial averages — individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight.² Browse our GLP-1 statistics for more figures.

05 · Tablets and injections

Injections and tablets

GLP-1 treatment comes as weekly injections and, more recently, as daily tablets. Our guide to oral GLP-1 weight loss explains the tablet options, and our oral and injection medication overview sets out the differences. For current Wegovy options, see the Wegovy pen page.

06 · Safety and interactions

What should not be taken with GLP-1 medicines?

Tell the prescriber about everything you take. Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed.⁷ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ Doses of insulin or sulfonylureas may need adjusting because of the risk of low blood sugar. Report any new symptom through the Yellow Card scheme.¹⁹ 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.

Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. Individual results vary. This page is information, not a substitute for medical advice.