SURMOUNT-2: how much weight tirzepatide took off in people with type 2 diabetes

SURMOUNT-2 tested tirzepatide for weight loss in adults who have both obesity and type 2 diabetes. Over 72 weeks, average weight fell 12.8% on the 10 mg dose and 14.7% on the 15 mg dose, against 3.2% on placebo [1]. That is a large, clear result, and it is smaller than the 20.9% seen at 15 mg in people without diabetes in SURMOUNT-1 [2].

Why this study matters

The authors open from the point that weight reduction is essential for improving health outcomes in people with obesity and type 2 diabetes [1]. SURMOUNT-2 reports the weight question for that group, which the main obesity trial left out by design [2].

We cover tirzepatide as a whole in our tirzepatide evidence guide, and the first obesity trial in SURMOUNT-1. This page takes the diabetes-population trial on its own.

What they did

Adults aged 18 or over with a body-mass index of 27 kg/m² or more and an HbA1c of 7% to 10% were randomly assigned one to one to one to tirzepatide 10 mg, tirzepatide 15 mg or placebo. Participants, investigators and the sponsor were all masked to treatment [1].

Of 1,514 adults assessed, 938 were randomised and received at least one dose: 312 on 10 mg, 311 on 15 mg and 315 on placebo. At the start, average weight was 100.7 kg, BMI 36.1 and HbA1c 8.02%. In the sample, 76% were White and 60% were Hispanic or Latino [1].

Adults were assessed for eligibility between 29 March 2021 and 10 April 2023, and 1,514 were assessed [1]. The two co-primary end points were the percentage change in body weight from baseline and the share of people losing 5% or more. The main analysis used the treatment-regimen estimand, which counts everyone randomised regardless of whether they stopped treatment or began rescue diabetes medication [1].

What they found

All comparisons with placebo gave p below 0.0001 [1].

The authors describe the result as substantial and clinically meaningful reduction in bodyweight [1]. The comparison with SURMOUNT-1 is worth reading carefully. In that trial, adults without diabetes lost 20.9% at 15 mg and 3.1% on placebo [2]. In SURMOUNT-2, the 15 mg group lost 14.7% and placebo lost 3.2% [1]. The placebo figures are nearly identical (3.1% and 3.2%), and the drug figure is lower in people with diabetes. These are two separate trials with different populations and different designs, so the gap describes a pattern, and it is not a direct head-to-head test.

Safety reported

The most frequent adverse events with tirzepatide were gastrointestinal, including nausea, diarrhoea and vomiting. They were mostly mild to moderate, and fewer than 5% of people stopped treatment because of side effects [1].

Serious adverse events were reported by 68 people (7%) overall. Two deaths occurred in the tirzepatide 10 mg group, and the investigators did not consider them related to the study treatment [1]. The authors conclude that the safety profile was similar to other incretin-based therapies for weight management [1].

Caveats

• Sponsor. Eli Lilly and Company funded the trial, and several authors are Lilly employees and shareholders [1].
• Analysis choice. The headline figures use the treatment-regimen estimand, which includes people who stopped the drug or started rescue diabetes medication, so they describe the effect of being assigned to treatment, not of taking every injection [1].
• Who was in it. The sample was 76% White and 60% Hispanic or Latino, with a mean age of 54.2 years, so it does not describe every group living with type 2 diabetes [1].
• Length. The trial ran 72 weeks. What happens after that point was not tested here [1].

What it means in practice

The practical reading is about size and direction. Someone reading the table should see that the weight change in this trial was large next to placebo, that it was measured in a mostly White and Hispanic or Latino sample, and that every participant already had both conditions, since type 2 diabetes was an entry requirement. This is a weight trial in people who already have type 2 diabetes, and it reports the size of the weight change at two doses used in the study. It does not tell any individual what to expect, and it gives no guidance on starting, stopping or dosing. Those decisions sit with a prescriber who knows the person's history.

What is still open

• How weight and blood sugar move beyond 72 weeks in this population.
• How the result looks in groups that this sample under-represents.
• How the weight response in people with and without diabetes compares when both are studied in the same trial.

What this means

We read SURMOUNT-2 as a well-run, manufacturer-funded randomised trial that shows tirzepatide produces substantial weight loss in people with type 2 diabetes. The direction is clear and the size is large: 12.8% and 14.7% against 3.2% on placebo [1]. It is also smaller than the SURMOUNT-1 figure in people without diabetes, though the two trials were separate and cannot be compared directly [1,2]. To disagree with that reading, you would need a randomised trial in this population showing no difference from placebo, and this page does not rely on one.

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