Retatrutide's two-year trial data: what we learned at…

Retatrutide, developed by Eli Lilly, is a triple hormone receptor agonist. It activates three receptors simultaneously: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon.

Semaglutide (Ozempic, Wegovy) activates only the GLP-1 receptor. Tirzepatide (Mounjaro, Zepbound) activates both GLP-1 and GIP. Retatrutide adds glucagon receptor activation, which is thought to directly increase energy expenditure and promote fat breakdown in the liver — on top of the appetite-reduction effects shared by the GLP-1 and GIP pathways.

That additional mechanism is the leading hypothesis for why weight-loss percentages in the retatrutide trials exceed those seen with earlier GLP-1 drugs. But the precise contribution of each receptor pathway to clinical outcomes is still being studied.

TRIUMPH-1 is the pivotal Phase 3 obesity trial for retatrutide. The study enrolled 2,339 adults with obesity (without type 2 diabetes) who were randomized to retatrutide at 4 mg, 9 mg, or 12 mg weekly, or placebo. Lead investigator: Ania Jastreboff, MD, PhD, professor of medicine and pediatrics at Yale School of Medicine.

At 80 weeks, the primary endpoint results:

• 12 mg arm: average weight loss of 28.3% (~70 lb). 45.3% of participants lost ≥30% of body weight. 65.3% fell below a BMI of 30, dropping out of the obesity range — including more than a third of those who started the trial with severe obesity (BMI ≥40).
• 9 mg arm: average weight loss of approximately 26% (~64 lb)
• 4 mg arm: average weight loss of approximately 19%
• Placebo: average weight loss of 2.2%

TRIUMPH-1 also included two nested sub-studies: one in 574 participants with knee osteoarthritis and one in 243 with moderate-to-severe obstructive sleep apnea. In the osteoarthritis sub-study, retatrutide reduced the WOMAC pain score by up to 73.1% from baseline. In the sleep apnea sub-study, the apnea-hypopnea index (a measure of sleep apnea severity) was reduced by up to 60.6%.

A 104-week extension of TRIUMPH-1 was also presented at ADA 2026. At two years, the 12 mg arm averaged 30.3% weight loss. More than 85% of participants in the highest-dose group had lost at least 15% of body weight, and over a quarter had lost at least 35%.

Important note: The 104-week extension data presented at ADA 2026 is conference-reported and has not yet been published in a peer-reviewed journal as of the date of this article. These figures should be understood as preliminary until peer-reviewed publication occurs.

TRANSCEND-T2D-1 is the Phase 3 trial in adults with type 2 diabetes (HbA1c 7.0%–9.5%) who were managing their condition with diet and exercise alone, with a BMI of at least 23. The study enrolled 537 participants randomized to retatrutide at 4 mg, 9 mg, or 12 mg, or placebo, over 40 weeks. Results were simultaneously published in The Lancet at the time of the ADA 2026 presentation. Lead investigator: Harpreet Singh Bajaj, MD (Centricity Research, Brampton, Canada).

Blood sugar control (primary endpoint):

• 12 mg arm: HbA1c reduction of -1.94% versus -0.81% with placebo
• 9 mg arm: -1.86%; 4 mg arm: -1.69%
• Higher proportions of participants on retatrutide reached HbA1c targets of <7.0%, ≤6.5%, and <5.7% compared to placebo

Body weight (secondary endpoint):

• 12 mg arm: -15.3% (~36.6 lb) versus -2.6% with placebo; weight loss was continuing at the end of the treatment period

Dr. Bajaj described the magnitude of weight loss in people with type 2 diabetes as "staggering" — noting that people with diabetes typically lose less weight with medications than those without. The 15.3% figure in a type 2 diabetes population exceeded weight-loss results seen with earlier GLP-1 drugs in comparable populations.

Both trials showed improvements in cardiovascular risk markers alongside weight and blood sugar outcomes.

In TRIUMPH-1, retatrutide was associated at 80 weeks with reductions of:

• Up to 41.0% in triglycerides
• Up to 24.2% in non-HDL cholesterol
• Up to 12.3 mm Hg in systolic blood pressure
• Up to 24.1 cm in waist circumference

In TRANSCEND-T2D-1 (40 weeks):

• Up to 39.6% in triglycerides
• Up to 19.8% in non-HDL cholesterol
• Up to 6.4 mm Hg in systolic blood pressure
• Up to 12.4 cm in waist circumference

These findings are consistent with the cardiovascular risk improvements observed with other GLP-1 class medications. Whether retatrutide reduces the actual rate of cardiovascular events (heart attacks, strokes) is a question for dedicated cardiovascular outcome trials, which have not yet been completed.

Adverse events in both trials were broadly consistent with the GLP-1 drug class. The most common were gastrointestinal:

• Nausea: up to 42.4% of participants on 12 mg in TRIUMPH-1; up to 26.5% in TRANSCEND-T2D-1
• Diarrhea and constipation were also common in both trials
• Most GI side effects were mild to moderate and resolved during treatment

One signal not seen in earlier GLP-1 trials: urinary tract infections. In TRIUMPH-1, UTIs occurred in 7.5%–8.8% of participants on retatrutide versus 5.3% on placebo — predominantly in women. In TRANSCEND-T2D-1, the rates were lower (0.7%–2.9% with retatrutide versus 0% with placebo).

The mechanism behind the UTI signal is not yet understood. Dr. Jastreboff suggested it may relate to changes in hydration status associated with reduced food intake. This signal will require further study and monitoring in any future FDA review.

Several important questions remain unanswered by the current Phase 3 data:

• Long-term cardiovascular outcomes: Whether retatrutide reduces the rate of heart attacks and strokes (as semaglutide has been shown to do in the SELECT trial) has not been studied in a dedicated outcomes trial.
• What happens when treatment stops: Weight regain after stopping GLP-1 class medications is well documented. Whether the pattern differs with retatrutide has not been published.
• Who benefits most: The trial populations were broadly defined. Individual responses in real-world use will vary.
• The UTI signal: The mechanism and clinical significance of the elevated UTI rate require further investigation.
• Approval timeline: Eli Lilly has not announced an NDA submission to the FDA as of ADA 2026. There is no publicly confirmed approval timeline.

Retatrutide is not approved by the FDA for any indication anywhere in the world. Under US federal law, it cannot be used in compounding — it is not a component of any FDA-approved drug and has not been reviewed for safety or effectiveness by the FDA.

The FDA has issued warning letters to telehealth companies and active pharmaceutical ingredient (API) distributors for marketing or selling unapproved retatrutide. Despite this, investigative reporting by CBS News, the New York Times, and Public Citizen documented more than 120 websites selling or promoting retatrutide and at least 50 licensed clinics advertising it as of mid-2026.

Products marketed as "retatrutide" outside clinical trials have unverified purity and content. Some products have been found to contain different substances altogether. Poison center exposures attributed to unapproved retatrutide rose 265% in the first four months of 2026 compared to the last four months of 2025.

If you have seen retatrutide advertised by a clinic or online, this is not the same as accessing the drug through a legitimate clinical trial.

• How does what we know about retatrutide compare to the approved options available to me today?
• If I have seen retatrutide advertised by a clinic or online, how do I know whether what they're offering is FDA-approved?
• Am I eligible for a legitimate clinical trial for retatrutide or another investigational drug? (Search ClinicalTrials.gov by condition and location)
• Given the current approved options, what is the evidence-based treatment path that makes sense for my health profile?

• A peer-reviewed publication of the 104-week TRIUMPH-1 extension data
• An Eli Lilly NDA submission to the FDA
• FDA Prescription Drug User Fee Act (PDUFA) date — if and when one is set, that signals a review timeline
• Cardiovascular outcome trial data for retatrutide

Medical disclaimer: This content is for educational purposes only and is not medical advice. Always consult a licensed healthcare professional before starting, stopping, or changing any treatment.

Sources

• Medscape: "Retatrutide Data Show Dramatic Weight Loss, Other Benefits" by Miriam E. Tucker (June 7, 2026): medscape.com
• Eli Lilly press release, TRIUMPH-1 Phase 3 (primary results): https://www.prnewswire.com/news-releases/lillys-[triple-agonist](glossary:triple-agonist)-retatrutide-delivered-powerful-weight-loss-in-pivotal-phase-3-obesity-trial-302778859.html
• ClinicalTrials.gov — TRIUMPH-1 (NCT05929066): clinicaltrials.gov
• ClinicalTrials.gov — TRANSCEND-T2D-1 (NCT06354660): clinicaltrials.gov
• TRANSCEND-T2D-1, The Lancet (simultaneous ADA 2026 publication): thelancet.com
• FDA's concerns with unapproved GLP-1 drugs: fda.gov