The SURMOUNT trials in numbers

Six trials produced almost every tirzepatide weight statistic in circulation. This page lists each one with the figures from its primary publication and, where the label adds detail, from section 14 of the Zepbound label. Every figure is a treatment-regimen estimate at the trial's endpoint unless stated.

SURMOUNT-1: obesity without diabetes

Phase 3, double-blind, 2,539 adults with BMI 30 or more, or 27 or more with a weight-related complication, diabetes excluded. Randomised 1:1:1:1 to 5, 10 or 15 mg weekly or placebo for 72 weeks including a 20-week escalation. Baseline mean weight 104.8 kg, BMI 38.0.

*The 5 mg figure for 20% or more is from label Table 2 (30.0%); the paper reports the 10 and 15 mg figures. Adverse events caused discontinuation in 4.3%, 7.1%, 6.2% and 2.6% of the 5 mg, 10 mg, 15 mg and placebo groups. PubMed 35658024. Label Table 2 adds the 10% and 15% thresholds: 68.5%, 78.1%, 83.5% versus 18.8% lost 10% or more; 48.0%, 66.6%, 70.6% versus 8.8% lost 15% or more.

SURMOUNT-2: obesity with type 2 diabetes

Phase 3, double-blind, seven countries, 938 adults with BMI 27 or more and HbA1c 7% to 10%. Randomised 1:1:1 to 10 mg, 15 mg or placebo for 72 weeks. Baseline weight 100.7 kg, BMI 36.1, HbA1c 8.02%.

Least-squares mean weight change: -12.8% at 10 mg, -14.7% at 15 mg, -3.2% on placebo. Differences from placebo -9.6 points (95% CI -11.1 to -8.1) and -11.6 points (-13.0 to -10.1). Between 79% and 83% on tirzepatide lost 5% or more versus 32% on placebo. Discontinuation for adverse events under 5%; serious adverse events in 7% overall; two deaths in the 10 mg group judged unrelated to treatment by investigators. PubMed 37385275.

The gap between SURMOUNT-1 and SURMOUNT-2 at the same doses, roughly six percentage points, is the most-cited illustration that people with type 2 diabetes lose less weight on incretin drugs than people without.

SURMOUNT-3: after intensive lifestyle intervention

Double-blind, 579 adults who had already lost 5% or more in a 12-week intensive lifestyle programme, then randomised to maximum tolerated tirzepatide (10 or 15 mg) or placebo for 72 weeks. Additional weight change from randomisation: -18.4% with tirzepatide versus +2.5% with placebo, difference -20.8 points (95% CI -23.2 to -18.5). 87.5% versus 16.5% lost a further 5% or more. PubMed 37840095. Label section 6.1 notes discontinuation for adverse reactions of 10% versus 2% in this trial, higher than in the pooled trials.

SURMOUNT-4: what happens when you stop

Randomised withdrawal, 70 sites, 783 adults enrolled in a 36-week open-label lead-in at maximum tolerated dose; 670 who completed it were randomised to continue tirzepatide or switch to placebo for 52 more weeks. Lead-in weight loss 20.9%. From week 36 to week 88: -5.5% on continued tirzepatide versus +14.0% on placebo, difference -19.4 points (95% CI -21.2 to -17.7). 89.5% of those continuing kept at least 80% of their lead-in loss versus 16.6% on placebo. Over the full 88 weeks: -25.3% versus -9.9%. PubMed 38078870. Label section 14 adds that 93% of randomised participants were on 15 mg at the end of the lead-in and that mean weight fell from 107.3 kg to 85.2 kg over those 36 weeks. The stopping page works through what these numbers mean.

SURMOUNT-5: tirzepatide against semaglutide

Phase 3b, open-label, 751 adults with obesity and no diabetes, randomised to maximum tolerated tirzepatide (10 or 15 mg) or maximum tolerated semaglutide (1.7 or 2.4 mg) weekly for 72 weeks. Weight change -20.2% (95% CI -21.4 to -19.1) versus -13.7% (-14.9 to -12.6). Waist circumference -18.4 cm versus -13.0 cm. More participants on tirzepatide reached each of the 10%, 15%, 20% and 25% thresholds. Gastrointestinal events were the most common in both groups. PubMed 40353578. The design was open-label, which is the main caveat, and the comparison is worked through on tirzepatide vs semaglutide.

SURMOUNT-OSA: sleep apnea

Two 52-week double-blind trials in adults with moderate to severe obstructive sleep apnea and obesity: trial 1 in people not on PAP therapy, trial 2 in people on PAP. Maximum tolerated tirzepatide versus placebo. Baseline AHI 51.5 and 49.5 events per hour; BMI 39.1 and 38.7. Change in AHI at week 52: trial 1, -25.3 versus -5.3 events per hour (difference -20.0, 95% CI -25.8 to -14.2); trial 2, -29.3 versus -5.5 (difference -23.8, 95% CI -29.6 to -17.9). PubMed 38912654. Label Table 9 reports the percentage change in AHI as -50.7% versus -3.0% and -58.7% versus -2.5%. The full picture, including the December 20, 2024 approval, is on tirzepatide for sleep apnea.

Reading these numbers

Every trial paired the drug with a reduced-calorie diet and increased activity, and the placebo arms show what that alone produced under trial conditions: -3.1%, -3.2%, and in SURMOUNT-3 a regain. Treatment-regimen estimates include people who stopped the drug, so they understate the effect in people who stayed on it and overstate what a person who quits at week 10 should expect. And the trials tested 5, 10 and 15 mg; nothing here speaks to 7.5 or 12.5 mg as long-term doses. The weight-loss projection tool on FormBlends Calculators applies the SURMOUNT-1 arm averages to a starting weight, with those caveats attached. For plain-English digests of trials across the whole GLP-1 class, see FormBlends Research.