Is Mounjaro better than Ozempic?

If you’ve been researching weight loss treatments, you’ve probably come across Mounjaro and Ozempic. Both belong to a group of drugs known as GLP-1 receptor agonists and are among the most searched weight loss injections, helping you lose around 20% of your body weight (1).

But when considering a weight loss injection, what’s the difference? Is Mounjaro better than Ozempic? Well, a recent study has shown that Mounjaro (tirzepatide) causes more weight loss than Ozempic (semaglutide) (2). However, there’s much more to consider when understanding which treatment might be right for you, especially in the UK.

Let’s compare these two medications, explore recent scientific research, and help you decide not only which drug is “better” but which is the best option for you.

Mounjaro vs Ozempic: Key similarities and differences

Mounjaro and Ozempic have a lot in common. Both are injectable treatments that are administered once weekly. The drugs work by targeting the receptor of a hormone called GLP-1, which regulates blood sugar levels and appetite. By activating the GLP-1 receptor, the drugs slow digestion, reduce appetite and regulate insulin. Over time, this can help you lose weight (3).

These are their similarities, and there are also some key differences:

• Effectiveness: There has been some groundbreaking research recently that put Mounjaro vs Ozempic weight loss injections head-to-head to discover which was more effective. The study, named SURMOUNT-5, found that Mounjaro can cause a person to lose 47% more weight than Ozempic (more on below) (4).
• Drug action: Ozempic and Mounjaro work by activating GLP-1 receptors to slow digestion and make you feel fuller. However, Mounjaro also targets another receptor called GIP, which is involved in other metabolic pathways (5). This dual action appears to cause more weight loss with Mounjaro.
• Side effects: The side effects of Mounjaro and Ozempic are similar, including nausea, diarrhoea, constipation, heartburn, dizziness, and fatigue (6)(7). However, some side effects are more common with Mounjaro, and others are more common with Ozempic. You might find you get on with one drug better than the other.
• Licensing: Mounjaro is licensed for weight loss in the UK (8), but Ozempic for weight loss is not. The equivalent product for UK patients is Wegovy (9). What is the difference between Ozempic vs Wegovy? Nothing. Wegovy is the UK version of Ozempic and contains the same drug (semaglutide), only marketed under a different brand name.

Mounjaro vs Ozempic: The SURMOUNT-5 study

We’ve already mentioned the SURMOUNT-5 study (10), the most significant breakthrough in the Mounjaro vs Ozempic weight loss debate to date. This was the first head-to-head trial comparing two weight loss injections, tirzepatide (Mounjaro) and semaglutide (Wegovy/Ozempic).

In the study, the researchers took 700 adults and prescribed them either Mounjaro or Ozempic for weight loss. All participants took their assigned Ozempic/Mounjaro injection once weekly for 72 weeks, and the researchers monitored their weight throughout the process. The results of the study came out in December 2024 and were noticeable (11):

• Individuals taking tirzepatide lost an average of 20.2% of their body weight, compared to the semaglutide group losing an average of 13.7%.
• The participants taking Mounjaro also experienced a 47% greater relative weight loss compared to Wegovy by 72 weeks.

What does this mean? According to the results of this study, Mounjaro is “better” than Ozempic for weight loss; it’s more effective and helps weight drop off more quickly. However, it’s worth noting that while Mounjaro demonstrates superior results overall, semaglutide is still highly effective. Both the semaglutide and tirzepatide groups lost significant weight over the 72 weeks, and we constantly see real-world patients get excellent results with Wegovy.

Also, the study participants were obese or overweight adults with at least one health condition (such as high blood pressure, abnormal cholesterol balance, sleep apnoea, or heart disease). Notably, the participants did not have diabetes, meaning the results highlight Mounjaro’s effectiveness as a weight loss treatment rather than its role in managing diabetes.

Why do people switch from Ozempic to Mounjaro?

There are several reasons people might switch from Ozempic to Mounjaro:

• To get better results: For some, switching to Mounjaro weight loss injections can offer better results. Given the clinical evidence that shows Mounjaro is more effective, anyone who isn’t seeing success on Ozempic/Wegovy or whose weight loss seems to have plateaued might choose to swap drugs. However, improving your diet and exercise or adjusting your dose is usually recommended first. The same stands if Mounjaro stops working—take a look at your lifestyle habits and dose before switching or stopping medications.
• To minimise side effects: Although Mounjaro and Ozempic side effects are similar, some are more common on one drug than the other. For example, stomach pain is “very common” (affecting more than 1 in 10) with semaglutide but only “common” (affecting up to 1 in 10) with tirzepatide (12). If you’re suffering from nasty side effects on semaglutide, it might make sense to try Mounjaro and see if there’s any improvement.

That said, switching isn’t necessary for everyone. Many people successfully lose weight with Wegovy, and studies show that people maintain weight loss with semaglutide long-term (13).

If you’re seeing results on Wegovy, we recommend sticking with it. The most important thing is that it’s working for you. Besides, even if you switch medications, there is no guarantee you’ll see faster weight loss on Mounions. We all respond to drugs differently.

Does Mounjaro have more side effects than Wegovy?

As Mounjaro and Wegovy work on the GLP-1 receptor, the common side effects of both weight loss drugs are very similar and include (6)(7):

• Nausea
• Vomiting
• Diarrhoea
• Constipation
• Heartburn (indigestion)
• Abdominal cramping
• Pain at the injection site

These side effects are usually mild and improve as your body adjusts to the treatment. You might also notice side effects worsen if you increase your dose of Mounjaro or Ozempic/Wegovy. If they don’t go away over time or are severe enough to disrupt day-to-day life, you must speak to a doctor.

Both drugs also carry an extremely low risk of more serious adverse effects, but the exact side effects differ slightly. Pancreatitis, gallbladder inflammation (cholecystitis), and gallstones (cholelithiasis) are all possible (though extremely rare) side effects of Mounjaro (7). Wegovy, but not Mounjaro, slightly increases the risk of biliary disease (15).

So, does Mounjaro have more side effects than Wegovy? If counting more serious complications associated with the drug, yes. However, these are extremely rare, occurring in <1% of patients. In terms of the more common digestive side effects, most people will find similar experiences on both drugs (2). But remember: we all respond to drugs differently. Some people will get on better with Mounjaro vs Wegovy, and others with Wegovy vs Mounjaro. It’s about working together to find the best weight loss injection for you and your body.

How to get Ozempic or Mounjaro in the UK

If you want to start using Wegovy or Mounjaro for weight loss, the first step is to speak with a healthcare professional. Both medications are only available in the UK on prescription, so you’ll need to talk to a doctor. This ensures that your treatment plan is safe and tailored to you.

An expert can also help you with which is the best weight loss treatment for your unique situation, so if you’re still scratching your head over whether Mounjaro or Wegovy is better, don’t panic! Conversely, if you have a preference for one weight loss injection over the other, let your doctor know. If the treatment you want is suitable for you, you will be able to use the treatment you prefer.

You can use our online doctor service if you don’t want to make an appointment with your GP at your local surgery. This simplifies the process by:

• Connecting you with licensed UK doctors remotely.
• Assessing your situation based on your response to our online health consultation.
• Recommending and prescribing the most suitable weight loss injection for you.
• Delivering your prescribed weight loss injections to your door.

Anyone choosing to buy weight loss injections online must make sure they’re browsing at a registered online pharmacy. There have been cases of unsafe Ozempic pen sales in the UK, so it’s essential to use a licensed retailer (16). Also, remember that Ozempic isn’t approved for weight loss in the UK (the drug is only sold under the brand name Wegovy). Avoid any site selling Ozempic to UK customers looking to lose weight.

What is the best injection for weight loss: Ozempic or Mounjaro?

Choosing between Ozempic (Wegovy in the UK) and Mounjaro ultimately depends on what works best for you. Both are effective weight loss injections that can help you achieve a healthier future. Mounjaro offers a slight edge in terms of weight loss effectiveness, but Wegovy remains a popular and proven option with excellent outcomes for many people.

Beyond these two injections, there are other weight loss treatments to consider. Options like Orlistat, a prescription weight loss tablet that can give great results, can also support your journey, particularly if weekly injections aren’t the right fit for your lifestyle or preferences.

Whatever you want to achieve, we’re here to help. At Oxford Online Pharmacy, our online doctor service works together with you to find the weight loss treatment that suits you best. View our weight loss treatments or contact our team today.

References

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3. Collins L, Costello RA. Glucagon-like peptide-1 receptor agonists [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2024.
4. Phalguni Deswal. Lilly’s Zepbound wins the weight loss duel with Novo’s Wegovy [Internet]. Clinical Trials Arena. 2024 [cited 2025 Jan 14].
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6. Filippatos TD, Panagiotopoulou TV, Elisaf MS. Adverse Effects of GLP-1 Receptor Agonists. The Review of Diabetic Studies [Internet]. 2014;11(3-4):202–30.
7. Mishra R, Raj R, Ghada Elshimy, Zapata I, Kannan L, Priyanka Majety, et al. Adverse Events Related to Tirzepatide. Journal of the Endocrine Society. 2023 Jan 26;7(4).
8. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss [Internet]. GOV.UK. 2023.
9. DHSC Media Team. Accessing Wegovy for weight loss: Everything you need to know - Department of Health and Social Care Media Centre [Internet]. healthmedia.blog.gov.uk. 2023.
10. CTG Labs – NCBI. A Study of Tirzepatide (LY3298176) in Participants With Obesity or Overweight With Weight Related Comorbidities (SURMOUNT-5) [Internet]. clinicaltrials.gov. ‌
11. Eli Lilly and Company. Lilly’s Zepbound® (tirzepatide) superior to Wegovy® (semaglutide) in head-to-head trial showing an average weight loss of 20.2% vs. 13.7% [Internet]. Eli Lilly and Company. 2023.
12. Webster RK, Weinman J, Rubin GJ. How does the side-effect information in patient information leaflets influence peoples’ side-effect expectations? A cross-sectional national survey of 18- to 65-year-olds in England. Health Expectations. 2017 Jun 15;20(6):1411–20.
13. Ryan DH, Lingvay I, Deanfield J, Kahn SE, Barros E, Burguera B, et al. Long-term weight loss effects of semaglutide in obesity without diabetes in the SELECT trial. Nature Medicine [Internet]. 2024 May 13;30:1–9.
14. Smits MM, Van Raalte DH. Safety of Semaglutide. Frontiers in Endocrinology [Internet]. 2021 Jul 7;12.
15. MHRA warns of unsafe fake weight loss pens [Internet]. GOV.UK.