Trial review

Tirzepatide for Type 2 Diabetes

The glycaemic evidence

SURPASS-2 randomised 1,879 adults with type 2 diabetes to tirzepatide 5, 10 or 15 mg or semaglutide 1 mg for 40 weeks, with change in HbA1c as the primary endpoint. Tirzepatide produced greater reduction — 2.01 to 2.30 percentage points against 1.86 — with the effect rising across its dose range.

The comparator dose is the detail that matters. Semaglutide 1 mg is a diabetes dose; the weight-management dose is 2.4 mg. This trial answers a diabetes question at diabetes doses, and it is routinely miscited as evidence about weight management.

The cardiovascular evidence

SURPASS-CVOT randomised 13,299 participants to tirzepatide or dulaglutide over about 4.5 years and found tirzepatide non-inferior for major adverse cardiovascular events. It is by far the largest and longest trial in the tirzepatide programme.

Non-inferiority to an active comparator is not superiority, and it is not by itself demonstration of benefit against no treatment. The inference many readers draw requires an additional step — that dulaglutide's own placebo-controlled benefit transfers. That is a reasonable clinical inference and it is not what this trial measured.

What it does contribute is long-duration safety data in a very large population, which the shorter weight-management trials cannot provide.

Zepbound and Mounjaro: same molecule, different label

Tirzepatide is the active ingredient in both. Mounjaro is approved for type 2 diabetes, Zepbound for chronic weight management and obstructive sleep apnoea. Chemically a dose of each at the same strength is the same drug.

The difference is commercial and it is large. Lilly runs a self-pay programme for Zepbound at $299 to $449 by dose and none for Mounjaro — which is why our dataset contains Mounjaro at up to $2,048 a month through a platform while the same molecule is $299 direct under a different label.

Which product you are prescribed is a clinical decision driven by indication. The economics are worth discussing.

Where the newer combinations sit

REIMAGINE 2 reported CagriSema reducing HbA1c 1.91 points more than semaglutide alone with 14.2% weight loss in 2,728 adults with type 2 diabetes. SOUL reported oral semaglutide cutting major adverse cardiovascular events by 14% and heart failure events by 22% in 9,647 high-risk patients.

The category is moving quickly, and weight figures in diabetes populations are typically smaller than in populations without diabetes — which makes cross-trial comparison in this space particularly unreliable.

What this does not cover

Weight-management outcomes at weight-management doses; that is SURMOUNT-1 and SURMOUNT-5. People without diabetes. And compounded preparations, which appear in no SURPASS trial.

Questions readers actually ask