The first direct comparison between two of the most prominent weight-loss medications-Mounjaro (tirzepatide) and Wegovy (semaglutide)-has shown that Mounjaro delivers significantly greater weight loss, according to a landmark clinical trial presented at the European Congress on Obesity and published in the New England Journal of Medicine.
Mounjaro Outperforms Wegovy in Head-to-Head Trial
The trial enrolled 750 adults with obesity, each with an average starting weight of 113kg (nearly 18 stone). Participants were assigned to take the highest dose they could tolerate of either Mounjaro or Wegovy for 72 weeks. The results were striking: those taking Mounjaro lost an average of 20% of their body weight, compared to 14% for those on Wegovy.
Furthermore, 32% of people on Mounjaro managed to lose at least a quarter of their body weight, a milestone reached by only 16% of Wegovy users.Waist circumference also shrank more with Mounjaro, with an average reduction of 18cm compared to 13cm for Wegovy. Beyond weight loss, Mounjaro users saw greater improvements in blood pressure, blood sugar, and cholesterol levels.
How Do These Drugs Work?
Both Mounjaro and Wegovy work by targeting receptors in the brain that regulate appetite, effectively tricking the body into feeling full and reducing food intake. Wegovy (semaglutide) mimics a single gut hormone released after eating, flipping one “appetite switch” in the brain. Mounjaro (tirzepatide), however, mimics two hormones, which researchers believe explains its superior results.
Side Effects and Tolerability
Both medications were found to have similar side-effect profiles. Common side effects include nausea, constipation, diarrhoea, and headaches, most of which are mild and tend to diminish as the body adjusts to the medication. Some patients may find one drug more tolerable than the other, depending on individual factors such as gut sensitivity and pre-existing conditions.
Who Can Access These Drugs in the UK?
In the UK, both drugs are available through specialist weight-management services and can also be obtained privately. Wegovy is available on the NHS for those with a BMI of 27 or more and weight-related health conditions, while Mounjaro was approved for NHS use in December 2024, mainly for those with a BMI of at least 35 and at least one weight-related comorbidity.However, access to Mounjaro on the NHS remains limited, and private sales are reportedly outpacing those of Wegovy.
Expert Perspectives and Future Directions
Experts stress that while both drugs are valuable tools in the fight against obesity, Mounjaro may be especially beneficial for those with the most weight to lose. Dr Louis Aronne, who led the trial, noted, “The majority of people with obesity will do just fine with semaglutide (Wegovy), those at the higher end may ultimately do better with tirzepatide (Mounjaro)”.
Professor Naveed Sattar from the University of Glasgow highlighted that while many patients are satisfied with 15% weight loss, others seek the maximum possible reduction. He also pointed out that private sales of tirzepatide are now well ahead of semaglutide in the UK, a trend likely to accelerate following this study. It’s important to note that Wegovy is currently licensed for additional health benefits, such as reducing the risk of heart attack, while similar trials for Mounjaro are still ongoing.
The Road Ahead
Research into weight-loss medications is rapidly evolving, with higher doses, oral formulations, and new drug classes under investigation. While these pharmaceutical advances offer hope for more effective obesity management, experts caution that broader societal changes to promote healthier lifestyles remain crucial for long-term prevention.
In summary, this landmark trial positions Mounjaro as the most effective weight-loss drug currently available, though both medications offer substantial benefits and may be suited to different patient needs. Access in the UK is expanding, but individual suitability and ongoing research will continue to shape the landscape of obesity treatment.
