BACKGROUND: Retatrutide is a GIP, GLP-1, and glucagon triple hormone receptor agonist, under clinical development for type 2 diabetes, obesity, and related complications. We aimed to assess the efficacy and safety of retatrutide as a monotherapy in people with type 2 diabetes that is inadequately controlled by diet and exercise alone.
METHODS: In this 40-week, phase 3, randomised, double-blind, placebo-controlled trial at 48 sites in the USA, Mexico, and India, we recruited adults (aged ≥18 years) with type 2 diabetes that is inadequately controlled by diet and exercise alone, glycated haemoglobin (HbA) between 7·0% and 9·5% (53-80 mmol/mol), and BMI of at least 23 kg/m. Participants were randomly assigned (1:1:1:1) to receive retatrutide (4 mg, 9 mg, or 12 mg) or placebo by once-weekly subcutaneous injection. The primary endpoint was the change in HbAconcentration from baseline to week 40. A key secondary endpoint was the percentage change in bodyweight from baseline to week 40. This trial is registered with ClinicalTrials.gov, NCT06354660, and is completed. 1c1c2
FINDINGS: Between April 10, 2024, and April 21, 2025, 930 participants were screened and 537 (296 [55%] female and 241 [45%] male) were randomly assigned: 134 to retatrutide 4 mg, 133 to retatrutide 9 mg, 136 to retatrutide 12 mg, and 134 to placebo. Baseline mean age was 48·8 years (SD 12·1), mean HbAconcentration was 7·9% (SD 1·1), mean duration of diabetes was 2·5 years (SD 4·4), and mean BMI was 35·8 kg/m(SD 7·0). 490 (91%) participants completed the treatment period on study drug and 504 (94%) completed the study. For the treatment regimen estimand, the mean change from baseline in HbAconcentration was -1·69% (SE 0·11) with retatrutide 4 mg, -1·86% (0·10) with 9 mg, and -1·94% (0·08) with 12 mg, versus -0·81% (0·12) with placebo, resulting in estimated treatment differences versus placebo of -0·88% (95% CI -1·18 to -0·59) with retatrutide 4 mg, -1·04% (-1·32 to -0·76) with 9 mg, and -1·12% (-1·39 to -0·85) with 12 mg (all p<0·0001). The mean percentage change from baseline in bodyweight was -11·5% (SE 0·7) with retatrutide 4 mg, -13·9% (0·8) with 9 mg, and -15·3% (0·8) with 12 mg, versus -2·6% (0·5) with placebo. The most frequent adverse events with retatrutide were generally mild to moderate gastrointestinal events, which subsided over time. Study intervention discontinuations due to adverse events were 2-5% with retatrutide and 0% with placebo. No severe hypoglycaemia was reported. Two deaths occurred during the study, both in the retatrutide 4 mg group and unrelated to the study drug. 1c1c2
INTERPRETATION: Retatrutide showed significant improvements in glycaemic control and bodyweight reduction as a monotherapy in adults with type 2 diabetes that is inadequately controlled with diet and exercise alone, with an adverse event profile consistent with molecules with GLP-1 agonist activity, supporting its potential as an effective treatment for type 2 diabetes.
FUNDING: Eli Lilly and Company.
