Mounjaro vs Wegovy UK 2026: Which Weight Loss Injection Is Right for You?

What Are Mounjaro and Wegovy?

Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two leading prescription weight-loss injections available in the UK. Both belong to a class of medicines called GLP-1 receptor agonists, which work by mimicking gut hormones that regulate appetite and blood sugar — helping you feel fuller for longer and eat less.

Despite working in a similar way, there are meaningful differences between the two medicines in terms of mechanism, efficacy, dosing, and cost. This guide breaks down everything you need to know to make an informed comparison.

How Do They Work?

Wegovy contains semaglutide, which activates one receptor — the GLP-1 receptor. Mounjaro contains tirzepatide, which activates two receptors — GLP-1 and GIP. This dual action is thought to be why Mounjaro produces slightly greater weight loss on average in clinical trials.

Both medicines are administered as a weekly subcutaneous injection using a pre-filled auto-injector pen. Doses are started low and increased gradually over several months to minimise side effects.

Weight Loss Efficacy

Clinical trial data shows both medicines produce significant weight loss compared to placebo:

• Mounjaro (SURMOUNT trials): Average weight loss of 20–22% of body weight at the highest dose (15mg)
• Wegovy (STEP trials): Average weight loss of approximately 15% of body weight at 2.4mg

These are averages — individual results vary considerably based on starting weight, diet, activity levels, and adherence. Both significantly outperform older weight loss treatments.

Side Effects

The side effect profiles of Mounjaro and Wegovy are broadly similar, as both act on the GLP-1 receptor. The most common side effects include:

• Nausea (most common, especially when starting or increasing dose)
• Vomiting
• Diarrhoea or constipation
• Reduced appetite
• Fatigue

Side effects typically improve after the first few weeks as your body adjusts. Starting on a low dose and titrating slowly helps minimise discomfort.

Cost in the UK

Both medicines are available privately in the UK, with prices varying by dose and pharmacy. As a general guide:

• Mounjaro: approximately £120–£280 per month depending on dose
• Wegovy: approximately £200–£350 per month depending on dose

MedEazy compares prices from verified, GPhC-registered UK pharmacies daily so you can find the cheapest option for your specific dose. Compare Mounjaro prices or compare Wegovy prices.

NHS Availability

Both Mounjaro and Wegovy have received NICE approval for NHS use in England, though access remains restricted and rollout through specialist weight management services is gradual. Most people currently access both medicines privately. Speak to your GP to find out whether you may qualify for NHS provision.

Which Is Right for You?

There is no single right answer — the best medicine depends on your individual health profile, medical history, and what your prescribing clinician recommends. As a general guide:

• If maximum weight loss efficacy is the priority and you are eligible, Mounjaro's dual-action mechanism gives it a slight edge in trial data
• If you have previously used semaglutide (e.g. Ozempic for diabetes) and tolerated it well, Wegovy may be a natural continuation
• Cost may also be a deciding factor — use MedEazy to compare current prices before committing