Retatrutide

What is retatrutide?

Retatrutide is an investigational, once-weekly peptide that activates three receptors at once: GLP-1, GIP, and glucagon. That makes it the first "triple agonist" to reach late-stage obesity trials, and its early weight-loss numbers are the largest reported for any drug in this class. It is not FDA-approved. Phase 3 trials are underway, so everything here is trial data, not settled prescribing practice.

How retatrutide works

It builds on the tirzepatide idea and adds a third target. Alongside the GLP-1 and GIP receptors that suppress appetite and improve insulin response, retatrutide also agonizes the glucagon receptor. Glucagon activation increases hepatic fat oxidation and energy expenditure, which is a lever that pure GLP-1 or dual GLP-1/GIP drugs do not pull. In theory you get appetite suppression and a metabolic-rate effect together, which is the leading explanation for its outsized trial results and its interest for fatty-liver disease.

What the research shows

In a 48-week phase 2 obesity trial, the 12 mg dose produced an average weight loss of 24.2%, and the 8 mg dose 22.8%. For cross-trial context, semaglutide reached about 14.9% and tirzepatide about 20.9% in their own trials. Retatrutide has also shown benefit in early studies of type 2 diabetes and metabolic-associated steatotic liver disease. The caveat matters: these are phase 2 results, and there is no long-term cardiovascular outcomes data yet, unlike the approved GLP-1 drugs.

Dosage and how it is used

Because retatrutide is not approved, there is no official prescribing schedule. Trials used once-weekly subcutaneous injection with gradual dose escalation, testing 1, 4, 8, and 12 mg arms. The higher doses drove the biggest weight loss but also the most gastrointestinal side effects, following the same titration logic as the approved incretin drugs.

→ How to reconstitute retatrutide: calculator, units to draw & storage

Side effects and safety

The reported side effects are dose-dependent and mostly gastrointestinal, in line with the rest of the class: nausea, vomiting, and diarrhea, heaviest during escalation. Because the molecule adds glucagon agonism, trials have also watched heart rate and glucose closely. The honest bottom line is that the long-term safety profile is not yet established. There is no completed cardiovascular outcomes trial, and it has not cleared the regulatory bar that semaglutide and tirzepatide have.

• Research depth: growing, but phase 2. Human clinical trials: yes, ongoing.
• Not FDA-approved. Long-term safety and cardiovascular data are not yet available.
• Varies by jurisdiction; not approved for self-administration. Verify current status independently.

Frequently asked questions

References

• Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine, 2023.
• Retatrutide for Metabolic Dysfunction-Associated Steatotic Liver Disease: A Randomized Phase 2a Trial. Nature Medicine, 2024.