Survodutide SYNCHRONIZE-1 reports 16.6% weight loss plus large liver and visceral fat reductions

Boehringer Ingelheim reported that its investigational glucagon/GLP-1 dual agonist survodutide produced average weight loss of up to 16.6% after 76 weeks in the Phase 3 SYNCHRONIZE-1 trial, meeting both co-primary endpoints ^[1]. Full results were later presented at the American Diabetes Association's 2026 Scientific Sessions and published simultaneously in the New England Journal of Medicine, where a prespecified imaging substudy showed liver fat fell 63.1% and visceral fat 34.0% at the higher dose ^[2].

What the trial measured

SYNCHRONIZE-1 enrolled 725 adults with a BMI of 30 or higher, or 27 or higher with at least one weight-related complication, and excluded people with type 2 diabetes ^[2]. Participants were randomized to once-weekly survodutide titrated to 3.6 mg (n=241) or 6.0 mg (n=242), or placebo (n=242), plus diet and activity counseling, across 116 sites in 14 countries between November 2023 and February 2026 ^[2]. Mean starting weight was 108.8 kg (about 240 lb) and mean BMI was 37.9 ^[2].

The two headline numbers differ because they come from two different analyses. Under the efficacy estimand — which models what would happen if everyone stayed on treatment for the full study — weight fell 15.3% at 3.6 mg and 16.6% at 6.0 mg, versus 3.2% on placebo ^[1][2]. Under the treatment-regimen estimand, which counts people regardless of whether they stopped the drug or started something else, the reductions were 12.2% and 13.0% versus 5.4% on placebo ^[2]. Boehringer's April release said up to 85.1% of treated adults lost at least 5% of body weight under the efficacy estimand versus 38.8% on placebo ^[1]; the journal-level data reported 72.6% and 71.9% reaching that mark versus 46.3% on placebo, and 28.5% at the 6.0 mg dose losing at least 20% versus 6.6% on placebo ^[2].

In the MRI substudy of 25 participants per arm, lean body volume dropped only 9.8% at the 6.0 mg dose, meaning more than 89% of tissue lost was fat ^[2]. Waist circumference, a marker tied to visceral fat, also fell significantly ^[1].

Tolerability is the open question

Gastrointestinal side effects — nausea, vomiting, diarrhea, constipation — were the main problem and clustered during dose escalation ^[1][2]. GI events led to stopping treatment in 17.8% of the 3.6 mg group and 20.2% of the 6.0 mg group, versus 2.9% on placebo ^[2]. A discussant at ADA put overall premature discontinuation at 35% to 40% ^[2]. No deaths were reported, there were no confirmed cases of pancreatitis, pancreatic cancer or thyroid cancer, and heart rate rose 3.2 to 3.5 beats per minute at week 76 ^[2]. In a prior Phase 2 trial, 24.6% of patients had discontinued ^[4].

Investigators also flagged a limitation: placebo-group weight loss was higher than expected, and more than 16% of placebo participants reported using a prohibited GLP-1 medication while still enrolled ^[2].

Why it matters for patients

Survodutide is not approved anywhere, and its safety and effectiveness have not been established ^[1]. If it does reach the market, the trial suggests a different trade-off than existing drugs. On raw weight loss it looks comparable rather than superior: placebo-adjusted weight loss was 13.4%, versus 12.4% reported at week 68 for Wegovy (semaglutide) and 17.8% at week 72 for Zepbound (tirzepatide), though those figures come from separate trials that cannot be compared head-to-head ^[4]. The potential differentiator is organ fat — a companion 48-week trial, SYNCHRONIZE-MASLD, found 84.2% of treated participants had at least a 30% relative drop in liver fat and 61.0% reached liver fat below 5%, versus 24.3% and 5.7% on placebo ^[2].

The flip side is tolerability. Roughly one in five people stopped because of stomach symptoms ^[2], which matters for anyone weighing whether a drug will be something they can stay on. Whether flexible titration can improve that is not yet settled ^[4].

What happens next

Additional SYNCHRONIZE readouts, including trials in people with type 2 diabetes and cardiovascular or kidney risk, are expected during 2026 ^[1]. The Phase 3 LIVERAGE (about 1,800 adults) and LIVERAGE-Cirrhosis (about 1,590 adults) MASH trials are ongoing ^[1]. Boehringer also said a triple GLP-1/GIP/NPY2 agonist enters Phase 2 in mid-2026 ^[1]. No regulatory filing date has been announced.