Real-World Study: Mounjaro Outshines Ozempic in Weight Loss

In a groundbreaking real-world study, Eli Lilly's Mounjaro (tirzepatide) demonstrated superior weight loss compared to Novo Nordisk's Ozempic (semaglutide), both of which are popular drugs for treating type 2 diabetes and obesity. This study, published in JAMA Internal Medicine, marks the first head-to-head comparison of these two drugs using healthcare data from everyday clinical settings. The findings reveal that patients taking Mounjaro not only hit weight-loss benchmarks more consistently but also lost more weight overall compared to those taking Ozempic.

Mounjaro and Ozempic belong to a class of drugs known as glucagon-like peptide-1 (GLP-1) receptor agonists. These drugs work by mimicking natural hormones in the gut and brain that regulate blood sugar levels and appetite.

Previous clinical trials have shown that patients on Ozempic can lose up to 16% of their total body weight. Mounjaro, however, has delivered even more impressive results, with some patients shedding more than 20% of their body weight. Although these results from clinical trials were promising, they couldn't be directly compared due to differences in how the trials were conducted. This new real-world study, however, provides a direct comparison and suggests that Mounjaro is indeed more effective for weight loss.

The study found that over a one-year period, patients on Mounjaro were three times as likely to achieve a weight loss of 15% or more compared to those on Ozempic. The total weight loss was consistently greater for Mounjaro users across various intervals—three, six, and twelve months—with the difference between the two drugs widening over time. For instance, at three months, the average weight loss for Mounjaro was 5.9%, compared to Ozempic's 3.6%. By the one-year mark, Mounjaro patients had lost over 15% of their body weight, while Ozempic users had lost about 8%.

The study also examined the safety profiles of both drugs. GLP-1 drugs are known for their gastrointestinal side effects, including nausea, diarrhea, and vomiting. More severe complications like bowel obstruction, gastroparesis, and pancreatitis have also been reported. However, the study found no significant difference in the rates of moderate to severe gastrointestinal adverse events between Mounjaro and Ozempic.

In the UK, Ozempic is licensed to treat type 2 diabetes, not weight management on its own. The same medicine, semaglutide, is licensed for weight loss under the name Wegovy, with its own dosing schedule. Mounjaro is licensed for both type 2 diabetes and weight management. So if your main goal is losing weight, the realistic comparison is usually Mounjaro against Wegovy. Our guide to the differences between Mounjaro and Wegovy explains how the two compare.

Ozempic acts on one gut hormone receptor, GLP-1. Mounjaro acts on two: GLP-1 and GIP. Both hormones help control blood sugar and appetite after you eat, and targeting both is thought to be why tirzepatide tends to produce greater weight loss. In day-to-day use, both medicines slow how quickly your stomach empties, help you feel full sooner and quieten food cravings. Neither is a quick fix. Results build gradually as your dose increases.

Yes, broadly. Both are once-weekly injections given under the skin of your stomach, thigh or upper arm using a pre-filled pen. You take your dose on the same day each week, with or without food, and rotate the injection site each time. Each medicine starts at a low dose and steps up gradually, usually every four weeks, to give your body time to adjust. If you miss a dose, check the patient leaflet or ask your pharmacist.

Switching is possible, but plan it with a clinician rather than doing it on your own. Never take two of these medicines at the same time. A clinician will look at your current dose, how well you have tolerated it, your medical history and your goals before deciding whether a change makes sense and which dose to start on. If you have type 2 diabetes, speak to your GP or diabetes team first, as your other diabetes medicines may need reviewing too.

It can. Mounjaro may make oral contraceptives less effective. The MHRA advises using a barrier method, such as condoms, alongside the pill for four weeks after starting Mounjaro and for four weeks after each dose increase. Neither Mounjaro nor Ozempic should be used during pregnancy or while breastfeeding. If you are planning a pregnancy, tell your clinician early, as they will advise when to stop treatment beforehand.

Yes. For weight management, these medicines are meant to be used alongside a reduced-calorie diet and more physical activity, not instead of them. Because your appetite drops, prioritise protein, vegetables and fibre at each meal so you still meet your nutritional needs. Smaller portions and eating slowly can also ease nausea. Our Mounjaro diet plan has practical meal ideas.

This real-world study offers valuable insights into the effectiveness of Mounjaro and Ozempic for weight loss, especially in patients struggling with obesity. While both drugs are effective, Mounjaro appears to be the stronger option for those aiming to achieve significant weight loss. As the use of these drugs continues to evolve, ongoing research will be crucial in understanding their long-term impacts and optimising their use in clinical practice.