Retatrutide's first diabetes phase 3 shows 16.8% weight loss alongside A1C drops

Eli Lilly reported topline results on March 19, 2026, from TRANSCEND-T2D-1, the first Phase 3 trial of retatrutide in adults with type 2 diabetes ^[1]. The once-weekly injection met its primary goal and all key secondary goals, lowering average A1C by 1.7% to 2.0% and producing average weight loss of up to 16.8% (36.6 lbs) at 40 weeks compared with placebo ^[1].

What the trial measured

TRANSCEND-T2D-1 randomized 537 adults evenly to retatrutide 4 mg, 9 mg, 12 mg, or placebo ^[1]. Participants had type 2 diabetes for an average of 2.5 years, had not taken diabetes medications for at least 90 days, had never used insulin (except for gestational diabetes), and entered with A1C between 7.0% and 9.5% and a BMI of at least 23 ^[1]. At baseline, average A1C was 7.9%, average weight was 96.9 kg (213.6 lbs), and average BMI was 35.8 ^[1]. Everyone assigned to retatrutide started at 2 mg weekly and stepped up every four weeks to their assigned target dose ^[1].

Using the efficacy estimand — which models results as if everyone stayed on treatment and did not add other diabetes drugs — A1C fell 1.7% at 4 mg, 2.0% at 9 mg and 1.9% at 12 mg, versus 0.8% with placebo ^[1]. Weight dropped 11.5%, 15.5% and 16.8% respectively, versus 2.5% with placebo ^[1].

The treatment-regimen estimand, which counts everyone regardless of whether they stopped the drug or added other medicines, showed smaller weight effects: 11.5%, 13.9% and 15.3%, versus 2.6% for placebo ^[1][2]. A1C reductions were nearly identical under both methods ^[1]. Lilly said no weight-loss plateau appeared through 40 weeks ^[1], and reported improvements in non-HDL cholesterol, triglycerides and systolic blood pressure, though the 4 mg group's results were not controlled for statistical error on those measures ^[1].

Side effects and dropouts

The most common side effects at 4 mg, 9 mg and 12 mg were nausea (16.4%, 19.5%, 26.5% versus 3.7% on placebo), diarrhea (18.7%, 26.3%, 22.8% versus 4.5%) and vomiting (15.7%, 15.0%, 17.6% versus 2.2%), mostly during dose escalation ^[1]. Dysesthesia — an abnormal skin sensation — occurred in 4.5%, 2.3% and 4.4% of retatrutide groups versus 0.0% on placebo, and Lilly said these events were generally mild and mostly resolved during treatment ^[1].

Discontinuation because of side effects was 2.2%, 4.5% and 5.1% across the three doses, versus 0.0% on placebo ^[1]. J.P. Morgan analysts said the rate of side effects was higher than what Mounjaro (tirzepatide) showed in a similar trial, which partly offsets the efficacy ^[2]. Scotiabank's Louise Chen called it "the highest levels of weight loss we've seen from an obesity drug to date" in a group that typically loses less weight than people without diabetes ^[2].

For context, Reuters noted that in separate 40-week late-stage trials, Lilly's oral orforglipron (Foundayo) produced average weight loss of 7.9% and tirzepatide 13.1% ^[2]. A previous retatrutide trial showed average weight loss of 28.7% ^[2].

The summary circulating with this news that up to 40% of participants reached a normal A1C is not stated in Lilly's release or the Reuters report, so that figure is not confirmed by these sources.

Why it matters for patients

Retatrutide is investigational and legally available only to people enrolled in Lilly's clinical trials ^[1]. It is not approved, not in pharmacies, and has no price. Nothing here changes what is available today.

What the data add is a picture of how a three-receptor drug — GIP, GLP-1 and glucagon — may perform in type 2 diabetes, a group that has historically lost less weight on incretin drugs ^[1][2]. The two estimands matter: the higher 16.8% figure assumes people stay on the drug, while the 15.3% figure includes those who stopped or added other medicines ^[1]. Real-world results usually land closer to the second number.

The tolerability data are also worth watching. Gastrointestinal side effects rose with dose, and up to 5.1% of participants left the study because of side effects ^[1].

What happens next

Detailed results will be presented at the American Diabetes Association Scientific Sessions in June 2026 and published in a peer-reviewed journal ^[1]. The broader TRANSCEND-T2D program has enrolled more than 2,050 people across three registrational trials, with more results expected over the next year ^[1]. RBC Capital Markets analysts anticipate a 2027 launch ^[2]; no regulatory filing date has been announced.