SURMOUNT-3: trial summary, limitations and UK relevance

Key findings

SURMOUNT-3 used a two-phase design: a 12-week intensive lifestyle-intervention lead-in, then randomisation of participants who achieved ≥5% weight loss during lead-in to tirzepatide vs placebo for the 72-week treatment period. Randomised continuation of tirzepatide produced additional mean body-weight reduction versus placebo, on top of the already-reduced baseline set by the lead-in. The trial design demonstrates that lifestyle-driven weight loss can be substantially deepened by adding tirzepatide rather than plateauing. Placebo participants who completed lead-in also lost further weight, though at markedly lower magnitude. Reported numerical results are in the Nature Medicine 2023 publication.

Safety summary

GI events remained the dominant adverse-event class; no new safety signals reported beyond the wider SURMOUNT programme.

Limitations

• Lifestyle-lead-in design complicates direct comparison with non-lead-in trials.
• 72-week duration; durability and long-term safety remain to be established.

UK relevance

Demonstrates that incremental pharmacotherapy benefit on top of structured lifestyle intervention is achievable in the studied population, relevant to NHS specialist weight-management pathways.