Tirzepatide (Mounjaro) and semaglutide (for example, Wegovy for weight management) are different prescription medicines. In the SURMOUNT-5 trial, tirzepatide produced greater average weight reduction than semaglutide over 72 weeks in adults with obesity but without type 2 diabetes, using the maximum tolerated doses studied. The trial does not establish a dose-for-dose conversion or a universal switching schedule.
Different medicines
They have different active ingredients, product licences and dose schedules.
Head-to-head evidence
SURMOUNT-5 compared maximum tolerated doses over 72 weeks.
Not a conversion chart
Trial results do not provide a safe dose equivalence.
Prescriber-led switch
Do not overlap, swap or restart doses without clinical advice.
What the head-to-head trial found
SURMOUNT-5 was a phase 3b, open-label, randomised trial in adults with obesity but without type 2 diabetes. Participants received maximum tolerated tirzepatide (10 mg or 15 mg once weekly) or maximum tolerated semaglutide (1.7 mg or 2.4 mg once weekly) for 72 weeks. The study was designed to compare weight reduction, not to test how to switch an individual patient between the medicines.
At week 72, the reported mean percentage change in body weight was −20.2% with tirzepatide and −13.7% with semaglutide. The most common adverse events in both groups were gastrointestinal and were generally mild to moderate, occurring mainly during dose escalation. The trial was funded by Eli Lilly, the manufacturer of tirzepatide; that funding should be disclosed when interpreting the findings.
The results apply to the trial population and treatment conditions. They should not be presented as a guarantee of an individual outcome, as evidence that every patient will lose more weight with tirzepatide, or as a direct comparison of every dose and every semaglutide brand.
Important differences between the medicines
Tirzepatide activates both GIP and GLP-1 receptors. Semaglutide is a GLP-1 receptor agonist. Both are used alongside dietary and physical-activity measures, but their licensed indications, titration schedules, contraindications, precautions and product presentations differ.
Brand and indication matter. Wegovy is licensed for weight management; Ozempic is a semaglutide brand used for type 2 diabetes. A study of semaglutide at the obesity-treatment dose should not be casually described as a comparison with every Ozempic dose or every clinical use of semaglutide.
Both medicines can cause gastrointestinal adverse effects. The appropriate choice depends on the person’s medical history, treatment goals, other medicines, tolerability, contraindications, availability and clinical judgement. A higher average weight reduction in one trial does not make one medicine universally preferable.
Switching between tirzepatide and semaglutide
There is no universally validated milligram-for-milligram conversion between tirzepatide and semaglutide. Their doses are not interchangeable. SURMOUNT-5 was not a switching trial and does not support a conversion table or a fixed starting dose when changing treatment.
A prescriber should review the current medicine, last dose, treatment indication, adverse effects, other medicines and relevant clinical risks before planning a switch. The timing of the next medicine and its starting dose must follow the relevant product information and individual clinical assessment. Do not take both medicines together unless a specialist has explicitly directed a clinically justified plan.
If switching because of supply problems, side effects or cost, contact the prescriber or pharmacist rather than independently starting the alternative. A gap in treatment, dose restart or a change in diabetes therapy may require additional monitoring.
Safety considerations shared by both treatments
Both medicines can cause nausea, vomiting, diarrhoea, constipation and other gastrointestinal symptoms. Persistent vomiting or diarrhoea can lead to dehydration. Severe or persistent abdominal pain requires urgent medical assessment because pancreatitis is an important warning in product information.
People taking insulin or sulphonylureas may have an increased risk of hypoglycaemia when treatment is combined, and the prescriber may need to review those medicines. Tell the healthcare team about pregnancy plans, breastfeeding, other medicines and any planned anaesthesia or deep sedation.
Frequently asked questions
Does tirzepatide work better than semaglutide?
In SURMOUNT-5, tirzepatide achieved greater average weight reduction than semaglutide at the maximum tolerated doses studied in adults with obesity without type 2 diabetes. This does not predict an individual response.
Can I convert my Wegovy dose directly to Mounjaro?
No. There is no universal milligram-for-milligram conversion. A prescriber must plan the switch.
Can I take both medicines together?
Do not combine them unless a specialist prescriber has specifically directed this. They are not intended to be self-combined.
Does SURMOUNT-5 apply to people with type 2 diabetes?
The trial population excluded people with type 2 diabetes, so its numerical results should not be directly generalised to that group.
References
- 1.. Aronne et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5), New England Journal of Medicine (2025).
- 2.. Electronic Medicines Compendium. Mounjaro KwikPen 5 mg: Summary of Product Characteristics (current UK product information).
- 3.. NHS. Tirzepatide (Mounjaro): medicine information.
Clinical and regulatory disclaimer
This article is for general educational information. It is not a diagnosis, an individual prescribing recommendation or a substitute for advice from a qualified healthcare professional. Product information and NHS commissioning arrangements can change; readers should check the linked official sources and discuss personal decisions with their prescriber or pharmacist. Vetted Therapeutics does not sell or supply medicines. In the UK, contact NHS 111 for urgent medical advice or 999 for a life-threatening emergency.