Last medically reviewed: March 2026
Quick Summary:
- Wegovy (semaglutide) and Mounjaro (tirzepatide) are injectable medications approved for weight management.
- Both drugs mimic gut hormones to control appetite, but Mounjaro acts on two hormones (GIP and GLP-1), while Wegovy targets just one (GLP-1).
- Recent clinical trials suggest Mounjaro generally leads to greater average weight loss compared to Wegovy.
- NHS guidelines recommend using these medications alongside lifestyle changes as part of a broader weight management plan.
- Side effects are largely similar, with digestive issues being the most common.
- Factors like cost, availability, and individual response may affect your choice; always chat with your healthcare provider before starting treatment.
Obesity is still one of the biggest health issues in the UK, contributing heavily to problems like type 2 diabetes and heart disease. Lately, new meds have shaken things up in weight management, especially injectable options like Wegovy and Mounjaro. I get a lot of questions like: “Which works better — Wegovy or Mounjaro?”
So, I’m laying out the facts here—from how these drugs work to the latest trial results, side effects, costs, and what UK health bodies recommend—so you can get a clearer picture if you’re thinking about medical help to lose weight.
Getting to Know Wegovy and Mounjaro
Wegovy (Semaglutide)
Wegovy is semaglutide at a higher dose, functioning as a GLP-1 receptor agonist. It was originally designed for managing type 2 diabetes but later got approval for long-term weight management in adults with a BMI of 30 or above—or 27 with related health issues.
The NICE guidance explains that Wegovy is given as a weekly injection, starting at 0.25mg and slowly increasing until hitting a steady dose of 2.4mg weekly.
Mounjaro (Tirzepatide)
Mounjaro came onto the UK scene in 2024 and works a bit differently. It’s an injectable that hits both GIP and GLP-1 receptors, which could mean better insulin response and appetite control than just targeting GLP-1 alone.
The usual starting dose is 2.5mg once a week, which can be increased up to 15mg depending on how well you tolerate it and the results you see.
What Makes Their Mechanisms Different?
GLP-1 Receptor Activation
Both drugs trigger the GLP-1 receptors, which boost insulin release, slow down stomach emptying, and help curb your appetite through brain signalling. This effect helps you feel full and eat less.
Mounjaro’s Dual Action on GIP and GLP-1
Here’s the cool part: Mounjaro also activates GIP receptors along with GLP-1. GIP can improve insulin secretion and may even help your body burn fat and use energy more efficiently. Some studies hint this dual effect can lead to more weight loss and better blood sugar control.
What Does the Research Show?
If you want to know which one’s stronger, we need to look at clinical trials that compare weight loss, safety, and how people handle the meds.
Wegovy Trials
The STEP trials have been key to understanding Wegovy. A 2025 report in The Lancet Diabetes & Endocrinology showed people on 2.4mg weekly lost about 15% of their body weight over roughly 68 weeks, compared to placebo.
Mounjaro Trials
The SURMOUNT studies checked out Mounjaro’s effects. SURMOUNT-1, published in 2025 in The New England Journal of Medicine, found that at the top dose of 15mg, folks lost an average of 22.5% of their body weight over 72 weeks—quite a bit more than Wegovy’s results.
Comparisons Between the Two
There haven’t been many big UK trials directly comparing these drugs side by side, but meta-analyses suggest Mounjaro might deliver bigger weight drops, while side effects seem pretty similar.
| Feature | Wegovy (Semaglutide) | Mounjaro (Tirzepatide) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Administration | Once-weekly injection, 0.25mg to 2.4mg | Once-weekly injection, 2.5mg to 15mg |
| Average Weight Loss | ~15% over 68 weeks (STEP trials) | Up to 22.5% over 72 weeks (SURMOUNT trials) |
| Common Side Effects | Nausea, vomiting, diarrhoea | Nausea, vomiting, diarrhoea |
| NHS Approval for Weight Management | Yes; prescribed within supervised programmes | Approved in 2024; increasingly used in specialised centres |
| Cost (approximate UK private price) | £300-£350 per month | £350-£400 per month |
Side Effects and Safety
Digestive Issues
Both meds often cause stomach-related side effects like nausea, diarrhoea, constipation, or vomiting—especially when doses get bumped up. Luckily, these tend to be mild or moderate and usually fade with time.