PeptideDeepDiveWhat Is Retatrutide? Triple-Agonist Trial Results & FDA Status
Retatrutide is Eli Lilly’s investigational GLP-1/GIP/glucagon triple agonist. Phase 2 and Phase 3 trials have reported unusually large average weight reductions. However, no regulator has approved the drug, and patients cannot get it as a legitimate prescription medicine.
Retatrutide (LY3437943) is an investigational once-weekly drug that activates GIP, GLP-1 and glucagon receptors. In Phase 2, the 12 mg group lost an average of 24.2% of body weight at 48 weeks. Lilly later reported 28.3% average weight loss at 80 weeks in the 12 mg TRIUMPH-1 group. In addition, a BMI ≥35 extension subgroup reached 30.3% at 104 weeks. Retatrutide is still unapproved, and Lilly plans a US regulatory submission in Q1 2027.
The PeptideDeepDive Editorial Team checks claims against peer-reviewed trials, ClinicalTrials.gov and sponsor reports. Importantly, we label topline findings when a full peer-reviewed paper is not yet available. We do not list a clinician reviewer because we have not verified one. Finally, this guide is for education only and does not provide prescribing, sourcing or dosing advice.
What Is Retatrutide?
Retatrutide, also known as LY3437943, is an investigational once-weekly peptide-based medicine from Eli Lilly. It activates three metabolic receptors at the same time: GIP, GLP-1 and glucagon. That makes it a GLP-1/GIP/glucagon triple agonist. By comparison, semaglutide mainly targets GLP-1, while tirzepatide targets GIP and GLP-1.
The regulatory point is simple: retatrutide remains investigational. Lilly says no regulator has approved it, and legitimate access is limited to Lilly-sponsored trials. Therefore, products sold online as “retatrutide” do not have the same quality or regulatory status as the trial drug.
How Does Retatrutide’s Triple-Agonist Mechanism Work?
Retatrutide combines three metabolic signals. GLP-1 and GIP influence appetite, insulin release and blood-sugar control. Meanwhile, glucagon-receptor activity may also affect energy use and fuel metabolism. Researchers designed the triple-agonist approach to test whether that added signal can produce a different effect from single- or dual-receptor medicines.
However, receptor theory does not prove a clinical advantage on its own. Instead, randomized trials must show whether the mechanism leads to meaningful outcomes. Therefore, the Phase 2 and Phase 3 results matter more than the receptor theory alone.
What Do Retatrutide Weight-Loss Trial Results Actually Show?
The foundational Phase 2 obesity trial appeared in the New England Journal of Medicine in 2023. At 48 weeks, the 12 mg group lost an average of 24.2% of body weight, compared with 2.1% in the placebo group. Read the Phase 2 trial.
Phase 3 has since moved the evidence forward. However, the newest obesity findings remain sponsor-reported topline results rather than full peer-reviewed papers. In May 2026, Lilly reported 28.3% average weight loss at 80 weeks in the 12 mg TRIUMPH-1 group. In addition, a study-extension subgroup with a baseline BMI of at least 35 reached 30.3% average weight loss at 104 weeks.
Lilly also reported positive Phase 3 topline results from TRIUMPH-2 and TRIUMPH-3 in July 2026. For example, adults with obesity or overweight plus type 2 diabetes lost up to an average of 20.8% at 80 weeks in TRIUMPH-2. Meanwhile, adults with severe obesity and heart disease lost up to 22.6% at 80 weeks in TRIUMPH-3.
These averages are larger than those typically reported in major obesity trials of semaglutide and tirzepatide. However, cross-trial comparisons do not prove that retatrutide is better. Instead, a direct Phase 3 study must answer that question. TRIUMPH-5 is comparing retatrutide with tirzepatide, and ClinicalTrials.gov lists primary completion for December 2026.
Retatrutide vs Semaglutide vs Tirzepatide: How Do They Differ?
Targets GLP-1. For example, approved products include Wegovy for weight management and Ozempic for type 2 diabetes.
Targets GIP and GLP-1. In addition, approved products include Zepbound and Mounjaro, depending on indication and country.
Targets GIP, GLP-1 and glucagon. However, the drug remains investigational even as Phase 3 data continue to emerge.
The important distinction is evidence and approval status, not just receptor count. Semaglutide and tirzepatide are approved medicines with established labels and regulated supply chains. By contrast, retatrutide remains a development-stage drug. For a broader comparison, see our GLP-1 medicines compared guide.
What Side Effects Have Retatrutide Trials Reported?
Across Phase 2 and sponsor-reported Phase 3 results, the most common side effects have been gastrointestinal. For example, trials have reported nausea, diarrhea, vomiting and constipation. This pattern resembles the side-effect profile of other incretin-based medicines. However, higher doses and dose increases can affect tolerability, and some participants stopped treatment because of side effects.
The Phase 2 trial also found dose-related increases in heart rate. Those changes peaked earlier in treatment and then declined. Because retatrutide is still under study, longer Phase 3 and outcomes trials remain important for defining its safety profile.
Is Retatrutide FDA-Approved? 2026 Regulatory Status
Retatrutide is not FDA-approved, and no other regulator has approved it. Lilly’s July 2026 update says the company now has enough clinical data to support global submissions and plans a US filing in Q1 2027. Therefore, the accurate August 2026 status is “Phase 3 with positive topline results; regulatory submission planned,” not “approved” or “under FDA review.”
There is also no legitimate retail prescription version today. In addition, FDA has warned online sellers that market “retatrutide” as an unapproved new drug. Lilly also warns that products sold outside its trials may contain unknown ingredients, contaminants or the wrong amount of active ingredient.
For current development status, see Lilly’s retatrutide explainer. In addition, see the TRIUMPH-1 trial record.
What Is Still Unknown About Retatrutide?
- Full peer-reviewed reports for the newest Phase 3 obesity results, including detailed safety tables
- The result of the direct TRIUMPH-5 retatrutide-versus-tirzepatide trial
- Long-term heart and kidney outcomes from TRIUMPH-Outcomes
- Final FDA, EMA and MHRA decisions after Lilly files its regulatory package
- How well the drug works and how well people tolerate it outside controlled trials if regulators approve it
Overall, retatrutide is one of the most important obesity drugs now in development. Its Phase 2 and Phase 3 weight-loss results are notable. However, it is still an unapproved medicine under active study. Therefore, trial results, regulatory approval and real-world treatment should be treated as different stages.
Retatrutide FAQ
Is retatrutide FDA-approved?
No. The FDA and other regulators have not approved retatrutide. Lilly says it plans a US regulatory submission in Q1 2027.
How much weight did people lose on retatrutide in trials?
In Phase 2, the 12 mg group lost an average of 24.2% at 48 weeks. In addition, Lilly reported 28.3% average weight loss at 80 weeks in the 12 mg TRIUMPH-1 group. A BMI ≥35 extension subgroup averaged 30.3% at 104 weeks.
How is retatrutide different from semaglutide and tirzepatide?
Semaglutide mainly targets GLP-1, while tirzepatide targets GIP and GLP-1. By contrast, retatrutide targets GIP, GLP-1 and glucagon receptors, which makes it a triple agonist.
Is retatrutide better than tirzepatide?
We do not know yet. TRIUMPH-5 is directly comparing the two drugs in adults with obesity. However, ClinicalTrials.gov lists primary completion for December 2026, so no completed head-to-head Phase 3 result is available yet.
Can you get retatrutide prescribed or compounded?
No FDA-approved prescription product exists today. In addition, FDA has warned online sellers that market retatrutide products as unapproved new drugs. Lilly also says people should not use products that claim to be retatrutide outside Lilly-sponsored trials.
Are the 30% weight-loss figures the average for everyone?
No. The 30.3% figure comes from a TRIUMPH-1 extension subgroup with a baseline BMI of at least 35. By comparison, the main 12 mg group averaged 28.3% at 80 weeks.
References
- Jastreboff, A.M. et al. (2023), Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial, New England Journal of Medicine, 389:514–526.
- Eli Lilly and Company (2026), TRIUMPH-1 Phase 3 topline results — 28.3% mean weight loss at 80 weeks in the 12 mg group and 30.3% in a BMI ≥35 extension subgroup at 104 weeks.
- Eli Lilly and Company (2026), TRIUMPH-2 and TRIUMPH-3 Phase 3 topline results — July 2026 update and planned US regulatory submission in Q1 2027.
- ClinicalTrials.gov, TRIUMPH-1 (NCT05929066) — completed Phase 3 obesity trial.
- ClinicalTrials.gov, TRIUMPH-5 (NCT06662383) — Phase 3 retatrutide-versus-tirzepatide study.
- ClinicalTrials.gov, TRIUMPH-Outcomes (NCT06383390) — long-term cardiovascular and kidney outcomes trial.
- Eli Lilly and Company, What to know about retatrutide — current unapproved-status and counterfeit-product warning.
- U.S. Food and Drug Administration (2026), Gram Peptides warning letter — FDA described online retatrutide products sold by the firm as unapproved new drugs.