What do the 2025 tirzepatide studies actually tell us?

What did SURMOUNT-5 find, and why does it matter?

SURMOUNT-5 enrolled 751 adults with obesity but without type 2 diabetes, randomising them to either tirzepatide, a dual GIP and GLP-1 receptor agonist (at the highest tolerated dose, up to 15 mg weekly) or semaglutide 2.4 mg weekly. The trial ran for 72 weeks. Tirzepatide produced a meaningfully greater average weight reduction than semaglutide over that period. The study was open-label, meaning participants and researchers knew which medicine they were taking, which is a limitation worth acknowledging. Even so, SURMOUNT-5 is the most direct evidence base the field now has for comparing these two medicines, and it was published in the New England Journal of Medicine, a high-standards peer-reviewed journal.

Before SURMOUNT-5, NICE's appraisal of tirzepatide (TA1026, December 2024) relied on indirect comparisons across separate trial programmes. SURMOUNT-5 shifts that picture by providing head-to-head data. It's worth reading the NICE appraisal and its evidence review if you want the full picture of how the committee weighed tirzepatide against existing treatments, NICE TA1026 is publicly available and covers the evidence in detail.

One practical note: neither the trial nor NICE tells you which medicine is right for you personally. Tolerability, other health conditions and your medication history all feed into that decision, which is precisely what a prescriber works through.

How does SURMOUNT-5 compare with earlier tirzepatide trial data?

SURMOUNT-1, published in the NEJM in 2022, remains the cornerstone evidence for tirzepatide's weight-management effect. In that 72-week trial of 2,539 adults with obesity, participants on the 15 mg dose achieved an average body-weight reduction of around 20 to 21 per cent. SURMOUNT-5 sits alongside that, adding comparative context rather than replacing the absolute-effect picture SURMOUNT-1 established.

The wider tirzepatide clinical programme (combining the SURPASS diabetes trials and the SURMOUNT obesity programme) involved more than 10,000 participants across its trials. That scale matters for safety signal detection as well as efficacy. You can read more about the full range of Mounjaro's clinical trials if you want a broader view of how the evidence has built up since 2021.

The 2025 results didn't arrive in a vacuum. They came after NICE had already recommended tirzepatide for NHS use and after Eli Lilly had received its UK marketing authorisation for weight management. The picture for Mounjaro in June 2025, including what SURMOUNT-5 added, was a direct comparison that regulators and clinicians had been waiting for. For anyone reading forum discussions or news coverage, that context helps separate genuine research findings from enthusiastic overstatement.

What do the 2025 studies tell us about long-term use?

One honest gap in the 2025 evidence base: most headline trials ran for 72 weeks. That's substantial for a weight-management trial, but questions about very long-term outcomes (beyond three or four years) remain open. Ongoing long-term data on Mounjaro is an active area of research, and observational data from real-world prescribing will accumulate as NHS rollout broadens.

What the existing data does confirm is a pattern of weight regain when treatment stops without continued lifestyle support in place. The SURMOUNT programme trials were conducted alongside reduced-calorie diet and increased physical activity guidance, that wraparound element is not optional in the research protocol, and NICE's recommendation reflects it. NICE requires that tirzepatide is used alongside appropriate diet and activity support, and that if someone achieves less than five per cent weight loss after six months at their highest tolerated dose, continuing treatment should be reviewed.

If you're curious about how people are responding to the 2025 research in practice, the 2025 Mounjaro forum discussions reflect real patient experiences, though they're no substitute for clinical advice. Speaking to a prescriber remains the right way to interpret what any given study finding means for your specific situation.

Does the research change who might be eligible for tirzepatide in the UK?

The 2025 trials don't change the UK licensing criteria, those are set by the MHRA based on its own evidence review. Tirzepatide (sold as Mounjaro) is licensed for adults with a BMI of 30 or above, or 27 and above with at least one weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. Lower thresholds apply for some ethnic backgrounds under UK guidance. You can check the NHS overview of tirzepatide for a clear summary of who it is and isn't suitable for.

NICE's NHS eligibility criteria are separate from the licensed private criteria and considerably more restricted, BMI 35 or above plus at least one weight-related comorbidity for the initial cohort, with phased expansion ongoing through 2026 and 2027. For people who don't meet NHS thresholds, or who'd rather not wait, a private consultation through a regulated pharmacy is the alternative route. Understanding the cost picture for private tirzepatide in the UK is a reasonable next step if NHS access isn't currently an option.

A prescriber assesses the whole picture, not just a BMI number. The trial data tells us what tirzepatide can do on average across a population; the consultation is where that evidence gets applied to you. If you'd like to explore whether tirzepatide might be clinically suitable, the team at nume's free consultation is a straightforward way to start.