Eli Lilly’s experimental drug retatrutide produced unprecedented weight loss in a phase 3 trial, with results that approach those seen after bariatric surgery and exceed outcomes from existing GLP-1 medicines.
What retatrutide is
Retatrutide is a once-weekly injectable triple hormone receptor agonist that stimulates receptors for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. That contrasts with widely used drugs such as Ozempic and Wegovy, which primarily target only the GLP-1 receptor.
Key trial results (TRIUMPH-1)
The TRIUMPH-1 phase 3 trial tested three doses of retatrutide (4 mg, 9 mg, and 12 mg) over extended follow-up. At 80 weeks, average weight loss by dose was:
– 4 mg: 19% (about 47 pounds)
– 9 mg: 25.9% (about 64 pounds)
– 12 mg: 28.3% (about 70 pounds)
Participants receiving placebo lost an average of about 2.2% (roughly 5.5 pounds). In a longer look at 104 weeks, people who started with a BMI of 35 or higher averaged about 30.3% weight loss—approximately 85 pounds.
Clinical and cardiometabolic effects
Beyond large reductions in body weight, participants experienced meaningful improvements in several cardiometabolic risk factors, including waist circumference, cholesterol levels, and blood pressure. Investigators described the magnitude of weight loss and accompanying metabolic gains as clinically significant and potentially transformational for many patients with obesity.
Safety and tolerability
The most common adverse events mirrored those seen with GLP-1–based drugs: nausea, diarrhea, constipation, vomiting, and upper respiratory tract infections. Reports of dysesthesia and urinary tract infections were generally mild to moderate and typically resolved while treatment continued. Most participants were able to remain on therapy despite these side effects.
Expert perspectives and caveats
Clinicians and company leaders framed retatrutide as a promising, potentially first-in-class option that could expand treatment choices across different stages of obesity. Some obesity specialists noted the results appear more potent than currently available medications. At the same time, experts emphasize important caveats: long-term safety and durability still require more data, head-to-head comparisons with existing drugs are needed, and widespread use will depend on supply and insurance coverage. Because obesity is a chronic condition, continued treatment will likely be necessary for sustained benefit.
Where things stand
The TRIUMPH-1 findings mark one of the largest medication-driven weight losses reported to date and position retatrutide as a candidate to change how severe obesity is treated. Further studies and regulatory review will determine whether the drug becomes widely available and how it compares directly with other therapies in routine clinical care.