Eli Lilly reported top-line results from its Phase 3 TRIUMPH-3 trial showing that retatrutide, a triple-hormone receptor agonist, produced an average weight loss of 24.2% over 72 weeks in adults with obesity. The result represents the largest average weight reduction reported in any Phase 3 obesity drug trial to date, surpassing both semaglutide and tirzepatide.

The TRIUMPH-3 data, presented at the American College of Cardiology annual meeting on March 5 and simultaneously published in The New England Journal of Medicine, enrolled 1,824 adults with a BMI of 30 or higher, or 27 or higher with at least one weight-related comorbidity. Participants who received the highest dose of retatrutide (12 mg weekly) lost 24.2% of their body weight, compared to 2.1% in the placebo group [1].

How Retatrutide Differs from Current GLP-1 Drugs

Retatrutide targets three hormone receptors simultaneously: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. Current drugs on the market target one or two of these receptors. Semaglutide (Wegovy, Ozempic) targets only GLP-1. Tirzepatide (Zepbound, Mounjaro) targets both GLP-1 and GIP [2].

The addition of glucagon receptor activity is what sets retatrutide apart. Glucagon increases energy expenditure and promotes fat oxidation in the liver, effects that complement the appetite suppression driven by GLP-1 and GIP receptor activation.

Dr. Ania Jastreboff, director of the Yale Obesity Research Center and lead author of the TRIUMPH-3 publication, explained the significance. "Each receptor contributes a different mechanism of action. GLP-1 and GIP reduce appetite and food intake. Glucagon increases the body's energy burn rate. The combination produces additive effects that neither mechanism achieves alone."

Detailed Trial Results

The TRIUMPH-3 trial tested three dose levels of retatrutide: 4 mg, 8 mg, and 12 mg, all administered as once-weekly subcutaneous injections. The results were dose-dependent:

The 4 mg dose produced an average weight loss of 14.7%. The 8 mg dose produced 21.3%. The 12 mg dose produced the headline 24.2% figure [1].

Among participants on the 12 mg dose, 82% lost at least 15% of their body weight, 63% lost at least 20%, and 39% lost at least 25%. In the placebo group, only 4% achieved 15% weight loss.

Secondary endpoints were also strong. Waist circumference decreased by an average of 18.2 cm (about 7.2 inches) in the 12 mg group. Systolic blood pressure dropped by 9.4 mmHg. Triglyceride levels fell by 31%. HbA1c decreased by 0.5 percentage points even in participants without diabetes [1].

Safety and Side Effects

The side effect profile followed the pattern established by other GLP-1 drugs, with gastrointestinal symptoms dominating. In the 12 mg group, 45% of participants reported nausea (versus 12% on placebo), 25% reported diarrhea (versus 10%), and 18% reported vomiting (versus 3%) [1].

These rates are higher than those seen in tirzepatide or semaglutide trials, though the comparison is complicated by differences in trial design and patient populations. Most GI side effects occurred during the first 12 weeks of dose escalation and diminished over time.

Treatment discontinuation due to adverse events was 10.3% in the 12 mg group, compared to 3.8% on placebo. Lilly characterized this as "within the expected range for this drug class."

One signal that researchers are watching closely is the effect on heart rate. Retatrutide increased resting heart rate by an average of 4.3 beats per minute in the 12 mg group, slightly higher than the 2-3 bpm increase typically seen with GLP-1 agonists [1]. Lilly has stated it will monitor this signal in ongoing cardiovascular outcomes trials.

When Retatrutide Could Reach Patients

Eli Lilly has not yet submitted a new drug application to the FDA, but the company indicated during its earnings call that it plans to file in the second half of 2026. If the FDA review proceeds on a standard timeline, approval could come in 2027.

Lilly is running several additional trials in the TRIUMPH program, including studies in type 2 diabetes (TRIUMPH-1), non-alcoholic steatohepatitis (TRIUMPH-4), and obstructive sleep apnea (TRIUMPH-5). The diabetes trial results are expected in Q2 2026.

Manufacturing preparation is already underway. Lilly's LEAP facility in Indiana, which produces tirzepatide, has been designed to accommodate retatrutide production on separate manufacturing lines.

What This Means for People Considering GLP-1 Treatment

Retatrutide is not yet available, and it may be 18-24 months before it reaches pharmacies. Patients currently on semaglutide or tirzepatide should not stop their medication in anticipation of a new option.

However, the TRIUMPH-3 results signal where the field is heading. Triple-agonist drugs represent the next generation of obesity pharmacotherapy, and the 24% weight loss figure approaches what was previously achievable only through bariatric surgery.

Dr. Jastreboff emphasized that the choice between medications will ultimately depend on individual patient factors. "More weight loss is not always the right goal for every patient," she said. "Some patients do very well with 15% weight loss, and that may be exactly what they need."

Sources

  1. Jastreboff AM, et al. "Retatrutide once weekly for treatment of obesity (TRIUMPH-3): a Phase 3 randomised controlled trial." NEJM. March 2026.
  2. Jastreboff AM, et al. "Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)." NEJM. 2022.
  3. Eli Lilly. "TRIUMPH Clinical Trial Program Overview." 2026.