What is Wegovy? What is Mounjaro? A 2026 UK Guide

Weight loss injections are now one of the most-discussed topics in UK healthcare. Two names dominate the conversation: Wegovy and Mounjaro. Both are prescription-only medicines, both are available through the NHS and private services, and both have strong clinical evidence behind them. They are not, however, the same drug.

This article explains what they are, how they differ, what the evidence shows, and what UK access looks like in 2026.

What is Wegovy?

Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics the gut hormone GLP-1, which helps regulate appetite and blood sugar. The result is reduced hunger, slower gastric emptying, and increased feelings of fullness after meals.

Wegovy was licensed in the UK in 2021 for weight management in adults. According to <a href="https://www.nhs.uk/conditions/obesity/treatment/" target="_blank" rel="noopener noreferrer">NHS guidance on obesity treatment</a>, Wegovy may be prescribed for adults who have a BMI of 30 or above, or a BMI of 27 or above with a weight-related health condition such as high blood pressure or type 2 diabetes. It is always used alongside a reduced-calorie diet and increased physical activity.

What is Mounjaro?

Mounjaro contains tirzepatide, a newer molecule that acts on two hormone pathways rather than one. It is a dual GIP and GLP-1 receptor agonist, which means it targets both of the body's main incretin hormones. In practice, this has produced particularly strong weight-loss results in clinical trials.

Mounjaro has been licensed in the UK for type 2 diabetes since 2022, and was licensed by the MHRA for weight management in adults in November 2023. NICE recommended tirzepatide for NHS weight management in December 2024 under Technology Appraisal TA1026, with GP-led rollout beginning in June 2025.

How Wegovy and Mounjaro are taken

Both medicines are given as once-weekly self-injections using a pre-filled pen. Treatment starts at a low dose and is gradually increased over several weeks. This slow titration helps the body adjust and reduces the chance of gastrointestinal side effects. A healthcare professional should always demonstrate correct injection technique and sharps disposal before the first dose.

What does the clinical evidence show?

Both medicines have been studied in large, placebo-controlled phase 3 trials.

Semaglutide (Wegovy) was tested in the STEP programme. In the headline STEP-1 trial of 1,961 adults without diabetes, participants on semaglutide 2.4mg lost an average of around 14.9% of their body weight over 68 weeks, compared with 2.4% on placebo.

Tirzepatide (Mounjaro) was tested in the SURMOUNT programme. In SURMOUNT-1, a 72-week trial of 2,539 adults with obesity, participants lost an average of:

• 16.0% of body weight on 5mg
• 21.4% on 10mg
• 22.5% on 15mg

Placebo participants lost 2.4%. Later SURMOUNT trials, including SURMOUNT-3 and SURMOUNT-4, broadly reinforced these results.

Direct comparisons between the two drugs in clinical practice depend on individual factors, which is why suitability should always be assessed by a prescriber.

Safety and side effects

Both medicines share a similar safety profile, reflecting their overlapping mechanism on GLP-1 receptors. The most common side effects are gastrointestinal: nausea, diarrhoea, constipation, or stomach pain. These are usually mild to moderate and tend to settle as the body adjusts.

In January 2026, the MHRA updated its product information for GLP-1 and dual GLP-1/GIP medicines to highlight a small risk of severe acute pancreatitis. Anyone taking these medicines who experiences severe, persistent stomach pain (particularly if it radiates to the back, or comes with nausea and vomiting) should seek urgent medical attention. Suspected side effects can be reported to the MHRA via the Yellow Card scheme.

Full information on both medicines, including side effects and eligibility, is available on the NHS obesity treatment page.

How to access Wegovy and Mounjaro in the UK in 2026

Access depends on your clinical profile and, increasingly, where you live.

On the NHS, Wegovy remains restricted to specialist weight management services. Mounjaro is now being rolled out through GP practices as well, but access is tightly phased. In 2025/26, NHS eligibility for Mounjaro typically requires a BMI of 40+ (37.5+ for certain ethnic groups) plus four or more weight-related conditions. Criteria are expected to broaden from June 2026 and again from March 2027.

For patients who don't meet NHS criteria, both medicines are available through regulated private prescribing services. Any legitimate provider will be registered with the General Pharmaceutical Council (GPhC), require a full clinical assessment before prescribing, and dispense UK-sourced stock through the cold chain. If you want a detailed breakdown of the cost side, see our guide: what is the cheapest way to get Mounjaro in the UK?

Why professional support matters

Wegovy and Mounjaro are prescription-only for good reasons. They interact with other medicines, they are not suitable for everyone (including during pregnancy or breastfeeding), and dose titration has to be managed carefully to minimise side effects. A healthcare professional's assessment is the safeguard that ensures the right medicine, at the right dose, for the right patient.

At Foundry Health, our pharmacist-led programmes provide regulated access, step-by-step guidance, and ongoing support. Treatment decisions are led by UK-registered prescribers, and medicines are dispensed by our GPhC-registered pharmacy partner.

Check your eligibility for a Foundry weight management programme.

This content is for educational purposes only and is not a substitute for professional medical advice. Always consult a healthcare professional before starting or changing any prescribed medicine.