Retatrutide is making big news after strong research results from its Phase 3 clinical trial. The drug, which is being developed by Eli Lilly, is designed to treat obesity and overweight. What makes it different is that it targets three hormone pathways instead of just one.
In the large Phase 3 TRIUMPH-1 trial, retatrutide helped people lose large amounts of weight over 80 weeks. Some results were close to what doctors usually see with weight loss surgery.
Here is what we know so far.
What Is Retatrutide and How Does It Work?
Retatrutide is a once-weekly injection. It works by activating three hormone receptors in the body:
- GLP-1, which reduces appetite and slows digestion
- GIP, which helps control insulin and metabolism
- Glucagon, which increases energy use and fat burning
By targeting all three, retatrutide helps people feel full, eat less, and burn more energy. It also improves blood sugar levels and other markers of metabolic health.
Earlier Phase 1 and Phase 2 trials showed strong weight loss and improved blood sugar control. The Phase 3 trial now confirms these results in a much larger group of people.
Phase 3 TRIUMPH-1 Trial: Weight Loss Results
The TRIUMPH-1 study included 2,339 adults with obesity or overweight and at least one weight-related condition. Participants did not have diabetes. The study lasted 80 weeks.
Patients were randomly assigned to receive retatrutide at 4 mg, 9 mg, 12 mg, or placebo.
At 80 weeks, the average weight loss was:
- 19.0% with 4 mg
- 25.9% with 9 mg
- 28.3% with 12 mg
- 2.2% with placebo
At the highest dose, people lost an average of about 70 pounds over 80 weeks.
Other important findings included:
- More than 60% of people on 12 mg lost at least 25% of their body weight
- About 45% lost at least 30% of their body weight
In an extension study lasting 104 weeks, people with more severe obesity lost an average of over 30% of their body weight.
These numbers are similar to results seen with some types of bariatric surgery.
Improvements Beyond Weight Loss
Retatrutide did more than just lower body weight. Participants also showed improvements in:
- Waist size
- Blood pressure
- Triglycerides
- Cholesterol levels
- Inflammation markers
Earlier studies also showed benefits in:
- Lowering HbA1c in people with type 2 diabetes
- Reducing liver fat
- Improving fatty liver disease markers
In one Phase 2 study, high doses reduced liver fat by more than 80% in some patients. This suggests the drug may help treat metabolic liver disease as well.
Side Effects and Safety
Like other drugs in this class, the most common side effects were stomach-related. These included:
- Nausea
- Diarrhea
- Constipation
- Vomiting
Higher doses had more side effects. Some patients stopped treatment because of these symptoms. However, most side effects were mild to moderate and improved over time.
So far, the safety profile looks similar to other GLP-1–based medications. Long-term safety is still being studied in ongoing trials.
Why Retatrutide Could Change Obesity Treatment
Retatrutide stands out because it targets three hormone pathways at once. This triple action may explain the large amount of weight loss seen in trials.
Possible benefits include:
- Surgery-level weight loss without surgery
- Strong improvements in metabolic health
- Potential treatment for fatty liver disease
- Powerful blood sugar control
Still, some questions remain. Experts want to know more about:
- Long-term safety
- Cost and insurance coverage
- Effects on muscle mass and body composition
It is important that weight loss comes from fat and not from muscle. Future studies will look more closely at this.
The Bottom Line
Phase 3 results show that retatrutide leads to major weight loss, up to 28% over 80 weeks. It also improves blood pressure, cholesterol, and other markers of metabolic health.
If approved, retatrutide could become one of the most powerful medications ever developed for obesity treatment. Ongoing Phase 3 trials will help confirm its long-term safety and full benefits.
Sources:
- Eli Lilly and Company — Retatrutide Phase 3 Results Press Release
Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Accessed by: https://investor.lilly.com/node/54321/pdf
2. Biomolecules Review on Retatrutide
Katsi V, Koutsopoulos G, Fragoulis C, et al. Retatrutide — A Game Changer in Obesity Pharmacotherapy. Biomolecules. 2025;15(6):796. Available from: https://www.mdpi.com/2218-273X/15/6/796
