Retatrutide

Retatrutide is a new class of weight loss drug that goes further than anything that came before it. While the current generation of GLP-1 drugs like semaglutide targets one receptor, and tirzepatide targets two, retatrutide hits three — GIP, GLP-1, and glucagon receptors simultaneously. This triple mechanism is what makes it so powerful: each receptor contributes a different lever on your metabolism, and activating all three at once produces a stronger and broader effect than any single or dual combination.

Developed by Eli Lilly under the code name LY3437943, it's a once-weekly injection. A modification to its structure extends the drug's half-life to around six days, which is what allows that weekly dosing to work. In Phase 2 clinical trials, participants on the highest dose lost an average of 24% of their body weight over 48 weeks. That number jumped to 28.7% in the TRIUMPH-4 Phase 3 trial, making it the most effective obesity drug tested in a major clinical trial to date.

Beyond weight loss, the Phase 3 data showed some unexpected benefits — including a 75.8% reduction in osteoarthritis pain scores, significant normalisation of blood sugar in prediabetic participants, and improvements in cholesterol, blood pressure, and inflammatory markers. Researchers weren't necessarily expecting those outcomes, but they suggest that the metabolic reset triggered by retatrutide extends well beyond fat loss.

Retatrutide is not approved for use anywhere as of early 2026. It is in Phase 3 trials and Eli Lilly is expected to file for FDA approval in late 2026. One side effect that doesn't appear with older GLP-1 drugs is dysesthesia — a tingling or abnormal sensation — which occurred in about one in five patients on the highest dose. That is a signal being watched closely as the data matures.