Tirzepatide Trials: Weight and Diabetes

Weight Loss & Metabolism Research

Tirzepatide has one of the deepest trial records of any compound in the research-peptide catalogue. Three large, randomized Phase 3 trials, published in The Lancet, JAMA, and the New England Journal of Medicine, cover its effect on weight, on maintaining that weight, and on diabetes risk.

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Findings

• In a 72-week trial of adults with obesity and type 2 diabetes, tirzepatide produced average weight loss of up to about 15%, versus about 3% on placebo.
• People who stayed on it kept losing weight; those switched to placebo regained most of what they had lost.
• Three-year data shows sustained weight loss of close to 20%.
• Tirzepatide is an approved medication, so its evidence comes from large randomized trials.

SURMOUNT-2: weight reduction (Lancet, 2023)

This 72-week, double-blind, placebo-controlled Phase 3 trial enrolled 938 adults living with obesity and type 2 diabetes across seven countries, randomized to once-weekly tirzepatide 10 mg, 15 mg, or placebo. Both tirzepatide doses produced substantial and clinically meaningful bodyweight reduction versus placebo, with a safety profile consistent with the drug class.

SURMOUNT-4: keeping the weight off (JAMA, 2024)

After a 36-week open-label lead-in in which 670 participants lost a mean of 20.9%, they were randomized to continue tirzepatide or switch to placebo for 52 weeks. Those who continued lost a further 5.5%; those switched to placebo regained 14% — a 19.4-point difference. Overall, 89.5% of the continued-treatment group kept at least 80% of their earlier weight loss, versus 16.6% on placebo.

Three-year outcomes (NEJM, 2024)

In a 176-week trial of 2,539 participants with obesity (of whom 1,032 also had prediabetes), mean weight change was -19.7% on 15 mg, -18.7% on 10 mg, and -12.3% on 5 mg, versus -1.3% on placebo. Fewer participants on tirzepatide progressed to type 2 diabetes.

What tirzepatide is

Tirzepatide is a dual agonist: it activates both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. It sits between single-receptor compounds and the triple-receptor retatrutide, a comparison our retatrutide vs tirzepatide article lays out.

Frequently asked questions

How much weight did tirzepatide produce in trials?

In the SURMOUNT-2 Phase 3 trial of adults with obesity and type 2 diabetes, tirzepatide produced substantial, clinically meaningful weight reduction over 72 weeks versus placebo. In a separate 3-year trial, participants on 15 mg reached a 19.7% mean weight reduction.

Does the weight come back if tirzepatide is stopped?

The SURMOUNT-4 trial addressed exactly this. After a 36-week lead-in producing 20.9% mean weight loss, those who continued tirzepatide kept losing (a further 5.5%), while those switched to placebo regained 14%. Continued treatment maintained the loss; withdrawal reversed much of it.

Did tirzepatide affect diabetes risk?

In the 3-year trial of people with obesity and prediabetes, tirzepatide produced a markedly lower rate of progression to type 2 diabetes than placebo, alongside sustained weight reduction.

Sources: Garvey WT, et al. Tirzepatide for obesity in type 2 diabetes (SURMOUNT-2). Lancet. 2023;402:613-626. PMID 37385275. Aronne LJ, et al. Continued tirzepatide for weight maintenance (SURMOUNT-4). JAMA. 2024;331:38-48. PMID 38078870. Jastreboff AM, et al. Tirzepatide for Obesity Treatment and Diabetes Prevention. N Engl J Med. 2025;392:958-971. PMID 39536238.