Key takeaways

  • Retatrutide is an investigational drug. It is not approved by the FDA or any other regulator.
  • A phase 2 trial reported average weight loss of up to 24.2% at 48 weeks, and later phase 3 results have also shown large losses.
  • Products sold under its name outside of clinical trials are unregulated.

Retatrutide goes one step further than tirzepatide. On top of the GIP and GLP-1 receptors, it also activates the receptor for glucagon, a hormone that raises energy use and affects how the liver handles fat.

It is being developed by Eli Lilly, the maker of tirzepatide, and is still in clinical trials.

What have trials found so far?

The first major results came from a phase 2 trial published in 2023. Adults with obesity lost up to 24.2% of their body weight on average after 48 weeks, depending on the group.

Phase 2 trials are smaller and shorter than the trials regulators use to approve a drug. Since late 2025, Lilly has announced topline results from several larger phase 3 trials, also reporting large average weight loss. Most of those results have not yet been published in full in peer-reviewed journals. The company has said it plans to apply for FDA approval.

What are the known side effects?

  • Nausea, diarrhea and other stomach problems, as with other drugs in this class.
  • An increase in heart rate in some participants.
  • Long-term safety is not known yet. A trial looking at heart outcomes is still running.

Why approval status matters

Until a drug is approved, the only way to receive the real product is through a clinical trial. Products marketed under the retatrutide name elsewhere have not been checked by any regulator, and their contents and purity are unknown.

The bottom line

Retatrutide’s early numbers are striking, and it may well be approved in the coming years. For now it is an experimental drug with incomplete safety data.

References

  1. Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389:514-526.
  2. ClinicalTrials.gov. TRIUMPH phase 3 program listings.
  3. World Anti-Doping Agency. The Prohibited List.