A Phase III clinical trial, TRIUMPH-2, has evaluated the efficacy and safety of retatrutide, an experimental once-weekly injection developed by Eli Lilly to treat obesity and type 2 diabetes. The drug has attracted attention because it activates three hormone receptors involved in appetite regulation, glucose control and energy metabolism. Unlike semaglutide, which targets the glucagon-like peptide-1 (GLP-1) receptor, and tirzepatide, which targets both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors, retatrutide activates all three pathways, including the glucagon receptor.
How Retatrutide’s Triple-Action Mechanism Works
Retatrutide combines three complementary mechanisms that may help people manage body weight and blood sugar levels.
GLP-1 receptor activation: Helps regulate blood sugar, reduce appetite and promote feelings of fullness.
GIP receptor activation: Supports insulin responses and contributes to metabolic regulation and weight management.
Glucagon receptor activation: May increase energy expenditure and influence how the body processes stored energy.
Together, these mechanisms could help retatrutide deliver substantial weight loss while improving glucose control. However, researchers must continue evaluating its long-term benefits and safety.
Phase III Trial Reports Significant Weight Loss
The 80-week TRIUMPH-2 trial evaluated retatrutide in 1,152 adults living with obesity and type 2 diabetes. Researchers compared three weekly doses of the drug—4 mg, 9 mg and 12 mg—with a placebo. The randomised, double-blind, placebo-controlled study was designed to assess whether retatrutide could produce greater weight loss while improving blood sugar control and other measures of cardiometabolic health. To help participants adjust to treatment, researchers started dosing at 2 mg and increased it every four weeks until participants reached their assigned target dose.
At the end of 80 weeks, participants experienced the following average reductions in body weight:
| Treatment group | Average weight loss |
| Retatrutide 4 mg | 11.9% |
| Retatrutide 9 mg | 16.8% |
| Retatrutide 12 mg | 18.8% |
| Placebo | 5.1% |
Participants receiving the highest dose lost an average of approximately 20.7 kg (45.5 pounds), compared with the placebo group. Among participants with a body mass index (BMI) of 35 kg/m² or higher, the 12 mg dose produced an average weight reduction of 21.9%. Furthermore, 75% of participants receiving the highest dose lost at least 10% of their body weight, while nearly one-third lost 25% or more. The findings, published in The Lancet, highlight retatrutide’s potential as a treatment for people managing both obesity and type 2 diabetes.
Retatrutide Also Improves Blood Sugar Control
Beyond weight reduction, retatrutide improved several measures of metabolic health. The treatment reduced glycated haemoglobin (HbA1c), a marker of average blood glucose levels over approximately two to three months, by 1.4–1.5 percentage points across the treatment groups. By comparison, the placebo group experienced a reduction of 0.45 percentage points. Participants also showed improvements in several cardiometabolic risk markers, including waist circumference, systolic blood pressure and triglyceride levels. These findings are particularly relevant because obesity and type 2 diabetes often occur together and can increase the risk of cardiovascular complications. Consequently, treatments that address both weight management and blood sugar control may offer important clinical benefits.
Why Weight Loss Matters for People with Type 2 Diabetes
Managing obesity can be challenging for people with type 2 diabetes because the condition involves complex interactions between insulin resistance, glucose regulation, appetite and metabolism. Even a moderate reduction in body weight can improve metabolic health. In particular, losing 5–10% of body weight may help improve blood pressure, blood sugar levels and other cardiovascular risk factors. Medicines such as semaglutide and tirzepatide have already expanded treatment options for people with obesity and type 2 diabetes. However, average weight loss with these treatments is generally lower in people with type 2 diabetes than in those without the condition. Retatrutide’s triple-receptor mechanism could potentially help address this challenge. Nevertheless, direct comparisons between treatments require appropriately designed clinical trials, and results from separate studies should not be interpreted as definitive evidence that one drug is superior to another.
Digestive Side Effects Remain a Concern
Although retatrutide produced substantial weight loss, researchers also reported adverse events, primarily involving the digestive system.
The most frequently reported side effects included:
Diarrhoea: Reported in up to 34% of participants.
Nausea: Reported in up to 28% of participants.
Vomiting: Reported in up to 16% of participants.
Adverse events led 8–12% of participants in the two higher-dose groups to discontinue treatment, compared with 5% in the placebo group. These findings underline the importance of evaluating both treatment effectiveness and tolerability. Further research will help clarify the drug’s long-term safety profile and identify the patients most likely to benefit.
What the Findings Mean for Obesity and Diabetes Treatment
The TRIUMPH-2 results suggest that retatrutide could become an important addition to the treatment landscape for people living with obesity and type 2 diabetes. Its ability to target three hormone receptors may help deliver substantial weight loss alongside improvements in blood sugar control and selected cardiovascular risk markers. However, researchers still need to establish its long-term safety, effectiveness across broader patient populations and potential impact on obesity-related complications. As reported by Medical Xpress, retatrutide remains an investigational medicine, and the trial findings do not establish it as an approved treatment. Further clinical evaluation and applicable regulatory approvals are necessary before it can become a routine treatment option.