SYNCHRONIZE-2: Survodutide Reaches 13.1% Weight Loss in Type 2 Diabetes, and 18% Stopped for Side Effects

What was announced

SYNCHRONIZE-2 randomised 755 adults with obesity or overweight and type 2 diabetes to weekly survodutide at 3.6 mg or 6.0 mg, or placebo, for 76 weeks. Boehringer Ingelheim reported that it met both co-primary endpoints: percentage change in body weight, and the share of people losing at least 5%. By the company's figures, weight fell by up to 13.1% on survodutide against 3.1% on placebo, and up to 79.3% lost at least 5% of their weight against 32.7%. The results were presented at the European Association for the Study of Diabetes meeting in Milan and published the same day in the New England Journal of Medicine.

The diabetes measures moved with the weight. HbA1c fell by up to 1.21 percentage points from a starting average of 7.4%, against 0.03 on placebo. Up to 29.5% of people on survodutide reached an HbA1c below 5.7%, the normal range, against 4.0% on placebo, and waist circumference fell by 11.1 cm against 3.5 cm.

Read the footnote before the headline

Trials like this report two versions of the same result. The treatment-regimen estimand counts everyone as randomised, whether or not they kept taking the drug. The efficacy estimand estimates what would have happened if everyone had stayed on treatment for the full 76 weeks. Every headline figure above is the efficacy estimand, and the announcement's own footnote says its p-values for that estimand are nominal.

That matters more than usual here, because a sizeable share of people did not stay on treatment. The announcement does not give the treatment-regimen figure for weight loss. When the paper is readable, that number, and how far it sits from 13.1%, is the first thing worth checking.

The question left open in April

When the first phase 3 trial, SYNCHRONIZE-1, reported in April, our coverage named tolerability as the bigger unknown: an earlier phase 2 trial had seen about a quarter of participants stop, and the topline did not say whether phase 3 had done better. SYNCHRONIZE-2 now gives a number. Treatment discontinuation because of gastrointestinal adverse events was 18% on survodutide against 1.2% on placebo, with nausea, vomiting, diarrhoea and constipation the most frequent events, mostly mild to moderate.

Boehringer's explanation is that discontinuations usually happened during dose escalation, because the trial protocol allowed limited flexibility to manage side effects, and that current and upcoming trials use more flexible titration. That is the company's account of why the number is high, and it is a testable one; it has not been tested yet.

Why 13.1% and not 16.6%

SYNCHRONIZE-1, in adults without diabetes, reported up to 16.6% weight loss over the same 76 weeks. The lower figure in SYNCHRONIZE-2 is the expected direction: people with type 2 diabetes generally lose less weight on these drugs than people without it, and the announcement itself describes this as a population in which weight loss is typically more challenging. The two trials should be read side by side rather than against figures from other companies' trials, which used different populations, doses and estimands.

Where survodutide stands

Survodutide is investigational and approved nowhere. Boehringer says results from its cardiovascular outcomes trial, SYNCHRONIZE-CVOT, are expected later this year, and it has started a separate phase 3 trial focused on blood sugar control in type 2 diabetes. FDA has granted the drug Fast Track and Breakthrough Therapy designations, both for the liver disease MASH with fibrosis, not for obesity. Our survodutide entry sets out the phase 2 and earlier phase 3 evidence; it will add SYNCHRONIZE-2 as a study once the paper can be read in full.

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