SURMOUNT-3: tirzepatide after a 12-week intensive lifestyle programme

Most weight-loss trials start the drug on day one. SURMOUNT-3 asked a different question: if someone has already done the hard work of a lifestyle programme and lost weight, what does adding tirzepatide do next?

What the trial asked

Whether tirzepatide at maximum tolerated dose produces additional weight reduction in adults who had just lost at least 5 percent of their body weight through a 12-week intensive lifestyle intervention.

Design

Double-blind, placebo-controlled. After the 12-week lifestyle lead-in, participants who had lost 5.0 percent or more were randomised 1:1 to tirzepatide (10 or 15 mg, whichever they tolerated) or placebo, once weekly for 72 weeks. The primary analysis used the treatment-regimen estimand in the intention-to-treat population, so it counts participants regardless of adherence.

Who was enrolled

579 adults with a BMI of 30 or more, or 27 or more with at least one obesity-related complication, excluding diabetes, who cleared the 5 percent lead-in threshold. The PMC full text gives 287 in the tirzepatide group and 292 on placebo. The abstract does not state weight at randomisation.

Primary endpoint and result

Two coprimary endpoints, both measured from randomisation (the end of the lead-in) to week 72:

• Additional mean percent weight change: -18.4 percent (SE 0.7) with tirzepatide versus +2.5 percent (SE 1.0) with placebo. Estimated treatment difference -20.8 percentage points (95% CI -23.2 to -18.5; P less than 0.001).
• Additional reduction of 5 percent or more: 87.5 percent (SE 2.2) with tirzepatide versus 16.5 percent (SE 3.0) with placebo. The abstract reports an odds ratio of 34.6 (95% CI 19.2 to 62.6; P less than 0.001).

Read the placebo arm carefully. It went up. People who had lost weight through lifestyle alone regained, on average, 2.5 percent over the following 72 weeks even while the programme continued.

Key secondary results

The abstract does not list secondary endpoints. The full paper reports them; they are not repeated here because they are not in the abstract.

Adverse events and discontinuation

The most common adverse events with tirzepatide were gastrointestinal, mostly mild to moderate. From Table 3 of the PMC full text: adverse events led to treatment discontinuation in 30 of 287 (10.5 percent) on tirzepatide and 6 of 292 (2.1 percent) on placebo. Nausea was the most common reason (8.4 percent versus 1.4 percent). Serious adverse events: 17 (5.9 percent) versus 14 (4.8 percent). One death in each group. The paper itself notes that gastrointestinal events and discontinuation were modestly higher than in the 15 mg arm of SURMOUNT-1.

Funding and registration

Eli Lilly and Company. ClinicalTrials.gov NCT04657016.

What this trial does not show

• The headline -18.4 percent is additional to the lead-in loss, not total loss from day one. Do not add it to SURMOUNT-1 numbers or compare it directly with them.
• Because everyone randomised had already responded to lifestyle change, the population is selected. It says nothing about people who did not lose 5 percent in the lead-in.
• Only maximum tolerated dose (10 or 15 mg) was studied, without separate dose arms.
• It does not tell you what happens if tirzepatide is later stopped; that is SURMOUNT-4.

Where the numbers come from

PubMed abstract of the primary paper (PubMed 37840095) and the open-access PMC full text (PMC10667099), both fetched 4 September 2026. The semaglutide counterpart, with intensive behavioural therapy running alongside the drug from the start rather than before it, is STEP 3.