In the 72-week SURMOUNT-5 trial, participants assigned to tirzepatide lost more weight on average than those assigned to semaglutide. That is strong comparative evidence for the population and protocol studied. It is not personalised prescribing advice, a promise of an individual result or proof that a clinic offering one medicine is better than another.
What SURMOUNT-5 compared
SURMOUNT-5 was a phase 3b, open-label randomised trial funded by Eli Lilly. It enrolled 751 adults with obesity but without type 2 diabetes. Participants were assigned to tirzepatide or semaglutide and treated for 72 weeks, with each group moving towards the maximum dose they could tolerate under the study protocol.
This matters because it was a direct comparison within one trial. Looking across separate placebo-controlled studies is much less reliable: populations, follow-up and analysis can differ enough to make an apparent comparison misleading.
What the headline result means
At week 72, estimated average weight change was −20.2% with tirzepatide and −13.7% with semaglutide. The estimated average difference was 6.5 percentage points in favour of tirzepatide. Average waist-circumference reduction was also greater in the tirzepatide group.
Those figures describe group averages, not the result every participant had. They also come from a structured trial with eligibility criteria, planned escalation, scheduled follow-up and formal adverse-event recording. They should not be turned into an individual forecast or lifted into clinic advertising without those limits.
What the trial says about tolerability
Gastrointestinal events were the most common adverse events in both groups. Most were mild to moderate and occurred mainly while treatment was being escalated. That broad pattern does not establish which medicine is safer or more suitable for a particular person.
The current UK Summaries of Product Characteristics and patient leaflets remain the appropriate public sources for licensed indications, warnings, contraindications and adverse-effect wording. A comparison headline is not a substitute for a proper suitability assessment.
What the evidence cannot answer
- People outside the trial: the study did not include adults with type 2 diabetes, and its average result should not be stretched to every patient group.
- Longer-term outcomes: the comparison ran for 72 weeks; it does not settle what happens over many years or after treatment ends.
- Individual suitability: a larger average weight change cannot account for one person's medical history, treatment goals, tolerance or competing risks.
- Routine private care: a clinic's assessment, prescribing, dispensing and follow-up may not resemble a clinical-trial protocol.
- Clinic quality: medicine choice alone says nothing about who takes responsibility when circumstances or side effects change.
UK access is a separate question
NICE recommends semaglutide and tirzepatide for weight management within defined NHS criteria and service arrangements. Those technology appraisals are not a league table, and NHS recommendations are not the same as the rules and clinical decisions governing every private prescription.
For current UK product information, Wegovy contains semaglutide and Mounjaro contains tirzepatide. The eMC documents set out their respective licensed wording. Neither a brand name nor availability through a private service removes the need for an individual clinical assessment.
What to compare in a clinic instead
If a clinic leads with “which injection wins?”, bring the conversation back to care. Ask who assesses suitability, who prescribes, which pharmacy dispenses, what follow-up is included, how adverse effects are handled and what happens if treatment is ineffective or not tolerated.
A serious provider should be able to explain why an option may or may not fit an individual without treating one trial average as a sales promise. For the access and verification steps, read how to get semaglutide or tirzepatide in the UK safely.
Sources
- Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. New England Journal of Medicine. DOI: 10.1056/NEJMoa2416394; PubMed record.
- ClinicalTrials.gov. SURMOUNT-5 study record and protocol information (NCT05822830).
- electronic Medicines Compendium. Mounjaro UK SmPC and patient leaflet.
- electronic Medicines Compendium. Wegovy UK SmPC and patient leaflet.
- NICE. TA875: semaglutide for managing overweight and obesity.
- NICE. TA1026: tirzepatide for managing overweight and obesity.