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Is Mounjaro safe? What you need to know

is mounjaro safe

Mounjaro (tirzepatide) has been used to treat diabetes since 2022, but its approval as a weight loss medication is much more recent (1). With its rollout on the NHS having started in 2024 (2), many people are asking the same question: Is Mounjaro safe?

The short answer? Yes, for most people, it’s safe and well-tolerated. While Mounjaro might be new to the market, it belongs to a well-studied group of drugs called GLP-1 receptor agonists, which have been used for nearly two decades. This means we already have a wealth of safety data from similar medications, as well as rigorous clinical trials that specifically tested Mounjaro.

So, what does the research say? Let’s take a closer look.

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Is Mounjaro safe for weight loss?

Mounjaro is generally safe and well-tolerated (3). It may be a new weight loss medication for 2025, but GLP-1s have been used for years. The first GLP-1 drug for diabetes was approved in 2006, and the first GLP-1 drug for weight loss was Saxenda (Liraglutide) in 2014, followed by Wegovy.

Although these are different drugs, they work on the same GLP-1 receptors in the body, so we already know a lot about how they affect metabolism, digestion, and long-term health. However, Mounjaro is slightly different; it targets not only GLP-1 receptors but also another type of receptor called GIP (glucose-dependent insulinotropic polypeptide) receptors (4).

The dual action is what makes Mounjaro more effective than other weight loss injections (5), but it also gives it a slightly different safety profile compared to regular GLP-1s. But rest assured, before any new drug is approved in the UK, it must pass rigorous testing to meet safety standards set by the MHRA (6). Mounjaro was tested on thousands before approval, ensuring it is safe and effective.

What do the clinical trials say?

Mounjaro was first studied as a diabetes medication in over 6,200 patients across multiple trials, known as SURPASS 1 to 5 (4, 7-11). The results showed it significantly lowered blood sugar and led to noticeable weight loss, even though weight loss wasn’t the primary focus of these studies.

The weight loss seen in the SURPASS trials led researchers to look at the potential of Mounjaro as a weight loss drug in a new set of large-scale studies called SURMOUNT 1 and 2:

  • SURMOUNT 1 involved 2,539 overweight or obese adults without diabetes (12).
  • SURMOUNT 2 involved 938 overweight or obese adults with type 2 diabetes (13).

In both studies, participants taking Mounjaro lost significantly more weight than those taking a placebo, with some losing up to almost 22% of their body weight (12). Tirzepatide was also well-tolerated, with mostly mild digestive side effects and no major safety concerns (12-13).

These findings confirmed that Mounjaro is both safe and effective for weight loss, leading to its approval as a weight loss treatment.

Who can use Mounjaro?

While Mounjaro is considered safe, it’s not suitable for everyone. According to NICE guidelines (14), Mounjaro is only recommended for adults who:

  • Have a BMI of 35 or higher (or lower for certain ethnic backgrounds).
  • Have at least one weight-related health condition, such as high blood pressure or diabetes.
  • Are following a healthy diet and increasing their amount of physical activity.

There are also groups who should absolutely avoid taking Mounjaro, such as pregnant or breastfeeding women (due to lack of safety data) or those with severe kidney or liver disease (15).

Before prescribing Mounjaro, doctors will assess your medical history, current medications, and overall health to ensure it’s a safe option for you. It’s also essential to follow the correct Mounjaro dose, starting with a lower dose and gradually increasing to allow your body to adjust.

Is Mounjaro safe for long-term use?

Because Mounjaro is relatively new as a weight loss drug, long-term safety data is still limited. However, no major safety concerns have been identified so far. Many people continue taking Mounjaro long-term if they keep seeing results, while others may stop once they reach a healthy weight.

NICE also recommends that if a person hasn’t lost at least 5% of their starting weight after six months, treatment should be reassessed, as the Mounjaro risks may outweigh the benefits (14).

How safe is Mounjaro?

Like all medications, Mounjaro has potential side effects. Fortunately, the most common ones—such as nausea, vomiting, diarrhoea, constipation, heartburn, and headaches—are mild and usually improve over the first month of tirzepatide as your body gets used to the medication.

That said, there are some rare but serious Mounjaro risks, including:

  • Pancreatitis (may affect up to 1 in every 100 people who use Mounjaro)
  • Allergic reactions (may affect up to 1 in every 1000 people who use Mounjaro)

Mounjaro can also interfere with other medications because it slows down digestion, which may affect how some oral drugs are absorbed (15).

You can find the full list of side effects in the patient information leaflet. Your prescribing team will help you understand any risks based on your medical history.

Should you use Mounjaro?

For most people who meet the criteria, Mounjaro is a safe and effective weight treatment but only when used correctly and prescribed by a licensed healthcare provider.

If you’re considering Mounjaro for weight management, here’s what to keep in mind:

  • Only take it with a prescription from a licensed doctor and pharmacy
  • Buy Mounjaro safely and be cautious of counterfeit weight loss injections sold online
  • Follow lifestyle changes (healthy eating and exercise) alongside treatment
  • Watch for side effects and report any worries to your doctor

If you’re considering weight loss treatment, Oxford Online Pharmacy offers expert consultations with UK-licensed doctors. All prescriptions are safely managed through the online doctor service, giving you real advice from real professionals discreetly and conveniently.

Start your consultation today, or view our weight loss treatments for more information.

References

  1. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss [Internet]. GOV.UK. 2023.
  2. NICE. NICE describes how weight loss drug tirzepatide will be rolled out [Internet]. The National Institute for Health and Care Excellence. NICE. 2024.
  3. Liu L, Li Z, Ye W, Peng P, Wang Y, Wan L, et al. Safety and effects of anti-obesity medications on weight loss, cardiometabolic, and psychological outcomes in people living with overweight or obesity: a systematic review and meta-analysis. EClinicalMedicine. 2024 Dec 27;79:103020–0.
  4. Gettman L. New Drug: Tirzepatide (MounjaroTM). The Senior Care Pharmacist [Internet]. 2023 Feb 1;38(2):50–62.  
  5. 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.
  6. GOV.UK. More information about the MHRA – Medicines and vaccines [Internet]. GOV.UK. 2023.
  7. Rosenstock J, Wysham C, Frías JP, Kaneko S, Lee CJ, Fernández Landó L, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1): a double-blind, randomised, phase 3 trial. The Lancet [Internet]. 2021 Jul;398(10295):143–55.‌
  8. Frías JP, Davies MJ, Rosenstock J, Pérez Manghi FC, Fernández Landó L, Bergman BK, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. New England Journal of Medicine [Internet]. 2021 Jun 25;385(6).
  9. Ludvik B, Giorgino F, Jódar E, Frias JP, Fernández Landó L, Brown K, et al. Once-weekly tirzepatide versus once-daily insulin degludec as add-on to metformin with or without SGLT2 inhibitors in patients with type 2 diabetes (SURPASS-3): a randomised, open-label, parallel-group, phase 3 trial. Lancet (London, England) [Internet]. 2021 Aug 14;398(10300):583–98. ‌
  10. Del Prato S, Kahn SE, Pavo I, Weerakkody GJ, Yang Z, Doupis J, et al. Tirzepatide versus insulin glargine in type 2 diabetes and increased cardiovascular risk (SURPASS-4): a randomised, open-label, parallel-group, multicentre, phase 3 trial. Lancet (London, England) [Internet]. 2021 Nov 13;398(10313):1811–24.
  11. Dahl D, Onishi Y, Norwood P, Huh R, Bray R, Patel H, et al. Effect of Subcutaneous Tirzepatide vs Placebo Added to Titrated Insulin Glargine on Glycemic Control in Patients With Type 2 Diabetes: The SURPASS-5 Randomized Clinical Trial. JAMA [Internet]. 2022 Feb 8;327(6):534–45.
  12. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 2022 Jun 4;387(3).
  13. W Timothy Garvey, Frias JP, Jastreboff AM, Roux le, Sattar N, Aizenberg D, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. The Lancet. 2023 Jun 1;402(10402).
  14. NICE. Recommendations | Tirzepatide for managing overweight and obesity | Guidance [Internet]. Nice.org.uk. NICE; 2024.  ‌
  15. NICE. British National Formulary | Tirzepatide [Internet]. NICE.