Published August 27, 2026 · updated August 27, 2026 · regulatory and clinical facts last checked 2026-08-27 · medically reviewed by Dr. S. Shuwart, MD on August 27, 2026

Medically reviewed · August 27, 2026

Tirzepatide clinical trials: SURMOUNT and SURPASS results in plain language

What the phase 3 trials of tirzepatide found: weight change by dose, comparators, durations, discontinuation, and what the results do and do not say about compounded copies.

What tirzepatide is

Tirzepatide is a once-weekly injectable that activates both the GIP and GLP-1 receptors. It is approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management and for obstructive sleep apnoea in adults with obesity. The SURPASS programme tested it in type 2 diabetes; the SURMOUNT programme tested it for weight management. This page covers SURMOUNT.

SURMOUNT-1: adults with obesity, without diabetes

Design: 2,539 adults with a BMI of 30 or more (or 27 or more with a weight-related condition, excluding diabetes), randomised to tirzepatide 5, 10 or 15 mg weekly or placebo, all with lifestyle counselling, for 72 weeks.

Result: mean weight change of about −15% at 5 mg, −19.5% at 10 mg and −20.9% at 15 mg, against about −3% on placebo. Discontinuation because of adverse events was higher on tirzepatide than placebo, in the mid-single-digit percentages. The most common adverse events were gastrointestinal: nausea, diarrhoea, constipation and vomiting, mostly during dose escalation.

SURMOUNT-2: adults with obesity and type 2 diabetes

Design: 938 adults with type 2 diabetes and a BMI of 27 or more; tirzepatide 10 or 15 mg versus placebo for 72 weeks.

Result: about −12.8% at 10 mg and −14.7% at 15 mg versus about −3.2% on placebo. Weight loss in people with type 2 diabetes is consistently smaller than in people without, a pattern seen with semaglutide as well.

SURMOUNT-3: after intensive lifestyle intervention

Design: participants first completed a 12-week intensive lifestyle programme and those who lost at least 5% were randomised to tirzepatide (maximum tolerated dose) or placebo for 72 weeks.

Result: an additional weight change of about −18.4% on tirzepatide versus about +2.5% on placebo from randomisation.

SURMOUNT-4: what happens when you stop

Design: all participants took tirzepatide for a 36-week lead-in (mean loss about 20.9%), then were randomised to continue tirzepatide or switch to placebo for 52 weeks.

Result: those who continued lost a further ~5.5%; those switched to placebo regained about 14% of body weight over the year. This is the trial behind the statement that stopping the medication is followed by substantial regain for most people.

SURMOUNT-5: head to head with semaglutide

Design: adults with obesity without diabetes, randomised to tirzepatide (maximum tolerated dose, up to 15 mg) or semaglutide 2.4 mg for 72 weeks, open label.

Result: about −20.2% on tirzepatide versus about −13.7% on semaglutide. See the comparison page.

SURMOUNT-OSA: obstructive sleep apnoea

Design: adults with moderate-to-severe OSA and obesity, with and without positive airway pressure therapy, randomised to tirzepatide or placebo for 52 weeks.

Result: large reductions in the apnoea-hypopnoea index relative to placebo, the basis for the OSA indication.

What these trials do not show

They tested the approved product at labelled doses with lifestyle counselling in selected populations. They do not test compounded tirzepatide, microdose regimens, orally disintegrating or sublingual forms, or formulations with added vitamins; none of those has phase 3 evidence, and this site grades them separately on the formulation evidence grades. Trial averages also hide wide individual variation, and the trials’ exclusion criteria (for example, prior pancreatitis) matter for eligibility.

Safety headlines from the label

The Zepbound label carries a boxed warning about thyroid C-cell tumours seen in rodents and contraindicates use in people with a personal or family history of medullary thyroid carcinoma or MEN 2. Warnings include pancreatitis, gallbladder disease, hypoglycaemia with insulin or sulfonylureas, acute kidney injury associated with dehydration, and delayed gastric emptying. These are educational statements from the label, not advice about any individual.

Related: /evidence/semaglutide-clinical-trials/ /evidence/tirzepatide-vs-semaglutide/ /medications/tirzepatide/

Educational information, not medical advice. Decisions about GLP-1 medication belong with you and a licensed clinician who knows your history. Compounded medications are not FDA-approved. Report an error.