Eli Lilly’s Retatrutide: What is it?

According to the Centers for Disease Control (CDC), 41.9% of adults in the United States are considered obese. Because of this, the pharmaceutical industry continues to search for new medications that effectively and safely treat people with obesity. Based on the large weight loss seen in early clinical trials, pharmaceutical company Eli Lilly thinks its new medication retatrutide could be seen as an important milestone for obesity treatment. Retatrutide finished its Phase II trials, and Phase III trial results are expected by the beginning of next year.

Retatrutide works a little differently than Novo Nordisk’s Wegovy (semaglutide) and Saxenda (liraglutide), which are popular FDA-approved weight loss drugs.

How does retatrutide work?

Like GLP‑1 agonists used for weight loss and type 2 diabetes (T2DM), retatrutide is a once-weekly subcutaneous injection. It is sometimes referred to as a triple hormone or triple G tri-agonist. It stimulates three receptors to help regulate your blood sugar and reduce your body weight. Retatrutide is a glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide‑1 (GLP‑1) receptor agonist. It also works at the glucagon receptor.

By acting on the GIP and GLP‑1 receptors, retatrutide regulates blood sugar levels and slows digestion to help you feel full faster after eating. By targeting the glucagon receptor, it can help decrease your appetite while also increasing the number of calories you burn.

What are some common side effects of retatrutide?

As with all medications, retatrutide has some adverse effects. According to Eli Lilly, retatrutide is safe and well tolerated, with a side effect profile similar to Ozempic (semaglutide) and Mounjaro (tirzepatide).

The most common side effects are mild and gastrointestinal-related, including:

• Nausea
• Diarrhea
• Vomiting
• Abdominal pain

Other reported side effects include increased heart rate and headache.

How much weight loss has been seen with retatrutide?

Phase 2 trial results showed that people with obesity (BMI ≥ 30) but not diabetes lost up to 24% of their initial body weight in 48 weeks when combining weekly retatrutide injections with diet and exercise.

When will retatrutide be on the market?

With promising Phase II results, Eli Lilly is awaiting Phase III trial data expected by the end of 2025 or early 2026. After submitting for FDA approval, the review process typically takes 6–10 months, so retatrutide could be approved around the end of 2026. When available, discuss with your healthcare provider to see if retatrutide is right for you.

Sources

• Eli Lilly experimental obesity drug could beat rivals in total weight loss for patients. CNBC. Accessed July 1, 2025.
• Jastreboff, A. M., et al. Triple–hormone-receptor agonist retatrutide for obesity — a phase 2 trial. New England Journal of Medicine. 2023. Accessed July 1, 2025.