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Wegovy vs Mounjaro Side Effects: Expert Comparison

Published on: June 03, 2026

Understanding wegovy vs mounjaro side effects uk is essential before starting your weight loss journey. Both medications are GLP-1 receptor agonists licensed by the MHRA, but their side effect profiles differ in frequency, severity, and duration. As a UK-registered pharmacy with thousands of patient consultations, we've compiled this evidence-based comparison to help you make an informed decision with your prescriber.

Common Side Effects: Wegovy vs Mounjaro

Both Wegovy (semaglutide) and Mounjaro (tirzepatide) share a similar side effect profile because they target the GLP-1 pathway, which naturally slows gastric emptying and reduces appetite [1]. The most frequently reported side effects are gastrointestinal: nausea, diarrhoea, constipation, vomiting, and abdominal discomfort.

In the STEP 1 trial for semaglutide, 44% of participants experienced nausea, compared to 31% in the SURMOUNT-1 trial for tirzepatide [1][2]. However, severity and duration varied significantly between individuals, and most gastrointestinal symptoms reduced after the first 4-8 weeks as the body adapted to treatment.

Clinical data shows that side effects are dose-dependent for both medications. Starting at lower doses and gradually titrating upwards—as per UK prescribing guidelines—significantly reduces the risk of severe gastrointestinal symptoms [1][2]. Your UK prescriber will determine the appropriate escalation schedule based on your tolerance and weight loss progress.

Nausea and Vomiting: Which Causes More?

Nausea is the most commonly reported side effect for both Wegovy and Mounjaro, but incidence rates differ. In clinical trials, 44% of Wegovy patients reported nausea versus 31% of Mounjaro patients at comparable efficacy doses [1][2]. Vomiting occurred in approximately 24% of Wegovy users compared to 16% of Mounjaro users.

The difference may be attributed to tirzepatide's dual GIP/GLP-1 mechanism, which some researchers believe provides a more balanced effect on gastric motility [3]. However, individual responses vary considerably—some patients tolerate Wegovy better, while others find Mounjaro gentler on their digestive system.

Practical strategies to minimise nausea include taking the injection on an empty stomach, eating smaller meals throughout the day, avoiding high-fat foods, and staying well-hydrated. If nausea persists beyond 8 weeks or becomes severe, your UK prescriber may adjust your dose or recommend an alternative treatment.

Managing Nausea During Treatment

Most patients find that nausea improves significantly after the first month as their body adapts to the medication. Ginger supplements, smaller portion sizes, and avoiding lying down immediately after eating can help reduce symptoms. If nausea interferes with daily activities or prevents adequate nutrition, contact your prescriber immediately—dose adjustment or temporary treatment pause may be necessary.

Gastrointestinal Side Effects Beyond Nausea

Diarrhoea and constipation are common with both medications, though they affect patients differently. In STEP trials, 30% of Wegovy patients experienced diarrhoea, while 23% reported constipation [1]. SURMOUNT trials showed similar rates for Mounjaro: 27% diarrhoea and 21% constipation [2].

Abdominal pain and bloating occur in approximately 20-25% of patients on either medication, typically during dose escalation phases. These symptoms are usually mild to moderate and resolve within 2-4 weeks [3]. Severe or persistent abdominal pain, especially if accompanied by fever or vomiting, requires immediate medical attention to rule out pancreatitis—a rare but serious side effect.

Maintaining adequate fibre intake, drinking plenty of water, and establishing regular meal times can help regulate bowel movements. If constipation persists, gentle laxatives may be appropriate, but consult your pharmacist or prescriber before starting any new medication alongside your weight loss treatment.

Serious Side Effects: What to Watch For

While rare, both Wegovy and Mounjaro carry risks of serious adverse events that require immediate medical attention. Pancreatitis occurred in less than 0.2% of patients in clinical trials for both medications, but symptoms—severe abdominal pain radiating to the back, persistent vomiting, and fever—warrant emergency assessment [1][2].

Gallbladder problems, including gallstones and cholecystitis, were reported more frequently in patients losing significant weight rapidly. This is a consequence of rapid weight loss itself rather than a direct drug effect, but patients should be aware of symptoms: severe right-sided abdominal pain, yellowing of skin or eyes, and clay-coloured stools [3].

Thyroid C-cell tumours were observed in rodent studies, leading to a boxed warning for both medications. However, no causal relationship has been established in humans. Both Wegovy and Mounjaro are contraindicated in patients with personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 [1][2].

Hypoglycaemia Risk

If you're taking Wegovy or Mounjaro alongside other diabetes medications—particularly insulin or sulphonylureas—you may be at increased risk of low blood sugar. Symptoms include shakiness, sweating, confusion, and rapid heartbeat. Your prescriber will adjust your existing diabetes medications to minimise this risk, but always carry a fast-acting glucose source if you're on combination therapy.

Tolerability and Treatment Discontinuation Rates

Discontinuation rates due to adverse events provide insight into real-world tolerability. In STEP 1, 7% of Wegovy patients discontinued treatment due to side effects, compared to 6.2% in SURMOUNT-1 for Mounjaro [1][2]. These similar rates suggest comparable overall tolerability, though individual experiences vary widely.

Most discontinuations occurred during the first 12 weeks of treatment, coinciding with dose escalation. Patients who successfully reached maintenance doses typically experienced fewer and milder side effects thereafter [3]. This highlights the importance of gradual titration and close monitoring during the initial treatment phase.

At Cured Pharmacy, our UK prescribers conduct follow-up assessments to monitor your progress and adjust treatment if needed. If side effects become intolerable on one medication, switching to the alternative GLP-1 treatment may be appropriate—many patients who struggle with one medication tolerate the other well.

Long-Term Safety Data

Semaglutide has been used for diabetes management since 2017, providing several years of real-world safety data. Tirzepatide is newer, approved for weight loss in 2023, but its diabetes formulation (Mounjaro) has accumulated substantial safety evidence since 2022. Both medications have demonstrated acceptable long-term safety profiles in ongoing extension studies, with no unexpected adverse events emerging beyond the first year of treatment [3].

Wegovy vs Mounjaro Side Effects: Making Your Choice

Choosing between Wegovy and Mounjaro based on side effects alone is challenging because individual responses vary significantly. Clinical trial data suggests Mounjaro may cause slightly less nausea, but the difference is modest and may not apply to your specific situation [1][2].

Your decision should consider multiple factors: side effect profile, efficacy data, dosing convenience, cost, and personal medical history. Wegovy is available from £135.00 at Cured Pharmacy, while Mounjaro starts from £124.99 reflecting different market positioning and efficacy profiles. Both require once-weekly injections and gradual dose escalation.

During your free online consultation, our UK prescribers will review your medical history, current medications, previous weight loss attempts, and personal preferences. If you have a history of severe gastrointestinal conditions, one medication may be more suitable than the other. Your prescriber can also discuss strategies to minimise side effects regardless of which treatment you start.

Scientific References

1. Wilding, J. P. H., et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183 [accessed 13 August 2026]
2. Jastreboff, A. M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038 [accessed 13 August 2026]
3. Nauck, M. A., et al. (2021). GLP-1 Receptor Agonists in the Treatment of Type 2 Diabetes – State-of-the-Art. Molecular Metabolism, 46, 101102. https://doi.org/10.1016/j.molmet.2020.101102 [accessed 13 August 2026]
4. NHS. (2026). Tirzepatide: a medicine to manage type 2 diabetes and treat obesity. https://www.nhs.uk/medicines/tirzepatide/ Accessed 13 August 2026.
5. NHS. (2026). Overweight and obesity in adults. https://www.nhs.uk/conditions/overweight-and-obesity/ Accessed 13 August 2026.
6. NHS England. (2026). Weight management injections. https://www.england.nhs.uk/ourwork/prevention/obesity/medicines-for-obesity/weight-management-injections/ Accessed 13 August 2026.

Information on this page is for educational purposes only and is not medical advice. All prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting any new medication. Side effect frequencies are based on clinical trial data and individual experiences may vary. If you experience severe or persistent side effects, contact your prescriber or seek immediate medical attention.