Mounjaro crowned most effective weight loss jab — but is it the right one for you?
Ed Milner | Last update: 18th May 2025
Mounjaro has officially pulled ahead in the race for the most powerful weight loss drug on the market. A new study published in the New England Journal of Medicine shows it outperforms Wegovy by a significant margin — but experts warn that “most effective” doesn’t always mean “best” for everyone.
TL;DR:
- New head-to-head trial shows Mounjaro leads to 20% weight loss, compared to 14% with Wegovy
- Results come from a large international study of over 700 people with obesity
- Trial funded by Mounjaro’s maker, Eli Lilly, and published in the New England Journal of Medicine
- Mounjaro now confirmed as the most effective GLP-1 weight loss drug so far
- But effectiveness isn’t everything — side effects, cost, availability, and tolerability also matter
The study: Mounjaro vs Wegovy, head-to-head
In a landmark clinical trial funded by Eli Lilly, researchers compared tirzepatide (Mounjaro/Zepbound) with semaglutide (Wegovy) in people living with obesity, but without type 2 diabetes.
The 72-week trial included 709 participants across multiple countries. They were randomly assigned to take either tirzepatide (10mg or 15mg) or semaglutide (2.4mg), the maximum approved doses for weight loss.
The results, published in May 2025 in the New England Journal of Medicine, were decisive:
- People on Mounjaro lost an average of 26.6kg (20.1% of their body weight)
- People on Wegovy lost 19.9kg (13.7% of their body weight)
🔗 Read the full study in The New England Journal of Medicine
In other words, Mounjaro helped people lose 50% more weight on average than Wegovy — reinforcing its growing reputation as the “King Kong” of weight loss drugs.
Why is Mounjaro more powerful?
Mounjaro works slightly differently from Wegovy. While both are GLP-1 receptor agonists, tirzepatide activates two gut hormones — GLP-1 and GIP — while semaglutide only activates GLP-1. This dual action is thought to improve insulin sensitivity, increase satiety, and reduce appetite even more effectively.
According to Eli Lilly’s press release, the results confirm that tirzepatide “demonstrates superiority” over semaglutide for chronic weight management — a claim now backed by rigorous peer-reviewed data.
🔗 Read Eli Lilly’s announcement
But is Mounjaro the best option for you?
Even though Mounjaro has now been shown to be the most effective weight loss drug in clinical trials, that doesn’t mean it’s the best choice for every individual. Factors to consider include:
✅ Side effects: Mounjaro can cause stronger nausea, vomiting and diarrhoea in some users compared to Wegovy
✅ Availability: Wegovy is currently more widely available in the UK; Mounjaro supply is still limited
✅ Cost: Prices can vary significantly between brands and pharmacies, especially when paying privately
✅ Other conditions: People with certain health conditions or medications may tolerate one drug better than another
✅ Dosing schedule: Some users prefer one injection pen design over another for comfort or ease of use
Want help deciding? Read our guide:
🧭 Mounjaro or Wegovy? Which weight loss treatment is right for you?
The bottom line: A clear winner — but not a one-size-fits-all
There’s now little doubt that Mounjaro is the most effective GLP-1 weight loss drug currently available. For those looking to maximise weight loss, it’s a game-changer.
But we’re all different. For some, Wegovy might cause fewer side effects, be easier to access, or feel more manageable week to week.
The best approach? Talk to your doctor or healthcare provider, weigh up the pros and cons — and tune in to the SlimrChat community chats for real talk from people on the same journey.