Two Medications, Different Mechanisms
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both injectable weight loss medications approved in the UK, but they work in fundamentally different ways. Understanding these differences is key to making an informed choice with your prescriber.
Wegovy targets a single hormone receptor — GLP-1 (glucagon-like peptide-1). It mimics a natural gut hormone that signals fullness to your brain, slows stomach emptying, and reduces appetite. It has been available in the UK since 2023 and was one of the first dedicated weight management injections to receive NICE approval.
Mounjaro targets two hormone receptors simultaneously — GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). This dual action is believed to produce greater appetite suppression and improved metabolic effects. NICE approved Mounjaro for weight management in December 2024 (TA1026).
Clinical Trial Results: Head-to-Head Data
The strongest evidence comes from the SURMOUNT and STEP clinical trial programmes, both published in the New England Journal of Medicine.
- Mounjaro (15mg dose): 22.5% average body weight loss over 72 weeks in the SURMOUNT-1 trial (Jastreboff et al., NEJM 2022)
- Wegovy (2.4mg dose): 14.9% average body weight loss over 68 weeks in the STEP 1 trial (Wilding et al., NEJM 2021)
- Both medications significantly outperform lifestyle interventions alone (typically 2–5% weight loss)
Side Effects Compared
Both medications share similar gastrointestinal side effects — nausea, diarrhoea, constipation, and vomiting are the most common. These typically occur during dose escalation and improve as your body adjusts.
In clinical trials, Mounjaro showed slightly lower rates of nausea compared to Wegovy at equivalent efficacy doses. However, individual experiences vary significantly. The gradual dose titration schedule used with both medications is designed to minimise these effects.
The MHRA has issued guidance on GLP-1 medications and the risk of pancreatitis. Seek immediate medical attention if you experience severe, persistent abdominal pain while taking either medication.
Cost Comparison in the UK
As of February 2026, typical private prescription prices from UK online pharmacies are:
- Mounjaro: from £149/month (starting dose 2.5mg), rising to £250–300/month at higher doses
- Wegovy: from £155/month (starting dose 0.25mg), rising to £260–320/month at the maintenance dose of 2.4mg
- Both prices include online consultation fees at most providers
NHS Availability
Both Mounjaro and Wegovy have NICE approval for use within specialist weight management services on the NHS. However, real-world NHS access remains limited and varies by region. Mounjaro's NHS rollout began in March 2025 under a phased implementation plan guided by NHS England's interim commissioning policy.
Many patients currently access these medications privately through online pharmacies while waiting for NHS availability in their area. All providers listed on WhichWeightMeds.org are independently verified and GPhC-registered.
Which Should You Choose?
The right medication depends on your individual circumstances, medical history, and what your prescriber recommends. Here are some general considerations:
- If maximum weight loss is your priority, Mounjaro has shown greater average results in clinical trials
- If you have type 2 diabetes, both medications have benefits — but Mounjaro's dual mechanism may offer additional glycaemic control
- If cost is a major factor, prices are comparable, though Mounjaro starting doses tend to be slightly cheaper
- If you prefer an established track record, Wegovy has been available longer with more real-world UK patient data