Phase 3 — Tirzepatide (Mounjaro / Zepbound)
SURMOUNT-1: trial summary, limitations and UK relevance
Tirzepatide at the 5, 10 and 15 mg weekly dose arms produced larger percent body-weight reductions than placebo over 72 weeks in the studied population, with reported placebo-adjusted mean reductions in the published primary report (NEJM 2022). For the precise reported numerical results readers should consult the cited NEJM publication and the EMA EPAR for Mounjaro for weight management.
Key findings
Tirzepatide at the 5, 10 and 15 mg weekly dose arms produced larger percent body-weight reductions than placebo over 72 weeks in the studied population, with reported placebo-adjusted mean reductions in the published primary report (NEJM 2022). For the precise reported numerical results readers should consult the cited NEJM publication and the EMA EPAR for Mounjaro for weight management.
Safety summary
The most common reported adverse events were gastrointestinal (nausea, diarrhoea, constipation, vomiting), typically mild-to-moderate and concentrated in the titration phase. Discontinuation due to adverse events was reported as low but non-zero. Hypoglycaemia rates in non-diabetic participants were low.
Limitations
- Non-diabetic population — does not directly establish glycaemic-control benefit in T2D.
- 72-week duration cannot establish long-term safety, durability after discontinuation, or downstream cardiovascular outcomes.
- Active comparator versus other GLP-1 / dual agonists not included.
- Trial population may differ from UK NHS real-world weight-management referral cohorts.
UK relevance
Foundational evidence for the MHRA's licensing of tirzepatide (Mounjaro) for chronic weight management in adults with obesity (BMI ≥30) or overweight (BMI ≥27) with weight-related comorbidities.
- Does not establish cardiovascular outcome benefit in obesity (separate CVOT required).
- Does not prove suitability for any individual or for use outside the MHRA-licensed pathway.
- Does not prove durability of weight reduction after discontinuation.
Frequently asked questions
What body-weight reduction did SURMOUNT-1 report?
SURMOUNT-1 reported that tirzepatide at 5, 10 and 15 mg weekly doses produced larger mean percent body-weight reductions than placebo over 72 weeks in adults with overweight or obesity without type 2 diabetes. For the precise published numerical results, readers should consult the primary NEJM 2022 publication (Jastreboff et al.).
Does SURMOUNT-1 cover people with diabetes?
No. SURMOUNT-1 enrolled adults without type 2 diabetes. Its findings do not directly establish glycaemic-control benefit or weight-reduction magnitude in people with type 2 diabetes; the SURMOUNT-2 trial covered the T2D population separately.
Was SURMOUNT-1 placebo-controlled?
Yes. SURMOUNT-1 compared tirzepatide (5, 10 and 15 mg weekly) against a matching placebo subcutaneous injection over 72 weeks. It did not include an active comparator such as another GLP-1 or dual agonist, so it does not establish comparative effect versus other weight-management medicines.
Did SURMOUNT-1 establish cardiovascular benefit?
No. SURMOUNT-1 was a weight-management efficacy trial and did not measure cardiovascular outcomes. A dedicated cardiovascular outcome trial would be required to establish that benefit in obesity.
How long did SURMOUNT-1 run, and what are the limits of that duration?
SURMOUNT-1 ran for 72 weeks. That duration cannot establish long-term safety, the durability of weight reduction after discontinuation, or downstream cardiovascular outcomes.
Related peptide profiles
Related trials
Related conditions
Related mechanisms
Related safety signals
Sources are tagged by class. Regulatory documents, peer-reviewed publications and trial registry records are preferred. Manufacturer disclosures and conference material are accepted where peer-reviewed publication is not yet available; preprints are flagged.
- Peer-reviewed publicationJastreboff AM et al., Tirzepatide once weekly for the treatment of obesity. NEJM 2022.
- Regulatory document (MHRA/EMA/FDA)EMA EPAR — Mounjaro
- Trial registry recordClinicalTrials.gov NCT04184622