Wegovy vs Mounjaro: 7 Key Differences You Must Know (2026)

Wegovy vs Mounjaro is the most common comparison for anyone exploring prescription weight loss injections in the UK. In the rapidly evolving landscape of medical weight management, two names have emerged as frontrunners: Wegovy (semaglutide) and Mounjaro (tirzepatide). Both are once-weekly injections that have demonstrated remarkable effectiveness in helping individuals with obesity achieve significant weight loss. While they share similarities, they have distinct mechanisms, efficacy rates, and side effect profiles.

This guide provides a head-to-head comparison of Wegovy and Mounjaro, helping you understand the key differences in their effectiveness, how they work, cost, and side effects, so you can have a more informed discussion with your healthcare provider.

Wegovy vs. Mounjaro: At a Glance

Feature	Wegovy (Semaglutide)	Mounjaro (Tirzepatide)
Mechanism	GLP-1 Receptor Agonist	Dual GLP-1 and GIP Receptor Agonist
Primary Use (UK)	Chronic Weight Management	Type 2 Diabetes (also used off-label for weight loss)
Avg. Weight Loss	~15% over 68 weeks [1]	Up to 22.5% over 72 weeks [2]
Administration	Once-weekly subcutaneous injection	Once-weekly subcutaneous injection
Common Side Effects	Nausea, diarrhoea, constipation, vomiting	Nausea, diarrhoea, decreased appetite, vomiting
UK Availability	Fully approved and available for weight loss	Approved for diabetes; private weight loss use is common

How They Work: A Key Difference

The most significant difference between the two drugs lies in their mechanism of action.

• Wegovy (Semaglutide): Wegovy is a GLP-1 (glucagon-like peptide-1) receptor agonist. It works by mimicking the GLP-1 hormone that is naturally released in your gut after you eat. This hormone signals to your brain that you are full, reduces appetite, and slows down the emptying of your stomach.

• Mounjaro (Tirzepatide): Mounjaro is a first-in-class dual-action agonist, targeting both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP is another gut hormone that, in combination with GLP-1, appears to have a more powerful effect on appetite suppression and energy balance. This dual mechanism is believed to be the reason for Mounjaro’s higher reported efficacy in clinical trials.

Efficacy: Which is More Effective for Weight Loss?

Clinical trial data suggests that Mounjaro may lead to greater weight loss than Wegovy.

• In the STEP 1 trial, participants taking the highest dose of Wegovy (2.4mg) achieved an average weight loss of 14.9% of their initial body weight over 68 weeks. [1]
• In the SURMOUNT-1 trial, participants on the highest dose of Mounjaro (15mg) achieved an average weight loss of 22.5% of their body weight over 72 weeks. [2]

While direct head-to-head trials are ongoing, the existing data from separate studies indicates a potential efficacy advantage for Mounjaro. However, it is crucial to remember that individual results can vary significantly.

Side Effects: Are They Different?

Both medications share a very similar side effect profile, as their mechanisms are related. The most common side effects for both Wegovy and Mounjaro are gastrointestinal, including:

• Nausea
• Diarrhoea
• Vomiting
• Constipation
• Decreased appetite
• Abdominal pain

These side effects are most common when starting the medication and during dose escalations. They are typically mild to moderate and tend to subside as the body adjusts.

Cost and Availability in the UK

• Wegovy: Is fully licensed and widely available for weight management in the UK through both the NHS (with strict criteria) and private clinics. Private costs typically range from £150 to £350 per month.

• Mounjaro: Is currently licensed in the UK for the treatment of type 2 diabetes. While many private clinics offer it “off-label” for weight loss, it is not yet officially approved for this indication. Its price is comparable to Wegovy, often in the £200 – £400 per month range privately.

Frequently Asked Questions (FAQ)

1. If Mounjaro is more effective, why would anyone choose Wegovy?

Wegovy has been available for weight loss for longer and has a more extensive track record and body of real-world data. It is fully licensed for this indication, which can be a crucial factor for both patients and prescribers. Some individuals may also tolerate Wegovy better.

2. Can I switch from Wegovy to Mounjaro?

Switching between these medications should only be done under the guidance of a healthcare professional. They will be able to advise on the appropriate washout period and starting dose to ensure a safe transition.

3. Which one is right for me?

The best choice depends on your individual health profile, medical history, tolerance for side effects, and a discussion with your doctor. They will consider all factors, including the current licensing status and clinical evidence, to recommend the most appropriate treatment for you.

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