Retatrutide: The Triple-Agonist Drug That Could Redefine Weight Loss
If you've been following the GLP-1 space, you already know that semaglutide (Wegovy) delivers about 15% body weight loss and tirzepatide (Zepbound) pushes that to 22%. Now there's a drug in clinical trials that just posted 28.7% — nearly double the original Wegovy results. It's called retatrutide, and it could be the most significant advancement in obesity treatment since GLP-1s first arrived.
Retatrutide (development code LY-3437943) is being developed by Eli Lilly — the same company behind Mounjaro and Zepbound. It's currently in Phase 3 clinical trials and has not been approved by the FDA. Here's what the clinical data shows so far, and when it might become available.
What Makes Retatrutide Different: Three Receptors Instead of One
Current GLP-1 medications work by activating one or two hormone receptors. Retatrutide is a first-in-class triple agonist that simultaneously activates three:
| Receptor | What It Does | Drugs That Use It |
|---|---|---|
| GLP-1 | Reduces appetite, slows gastric emptying | Wegovy, Ozempic, Saxenda (all current GLP-1s) |
| GIP | Enhances insulin secretion, may increase thermogenesis | Zepbound, Mounjaro (dual agonists) |
| Glucagon (GCGR) | Increases metabolic rate, promotes fat burning | Retatrutide ONLY (first drug to add this) |
The glucagon receptor activation is the key differentiator. Glucagon increases your resting energy expenditure and promotes fat oxidation — essentially, your body burns more fat even at rest. This third mechanism may explain why retatrutide's weight loss numbers exceed anything seen before in clinical trials.
Clinical Trial Results: The Numbers
Retatrutide has been studied in both Phase 2 and Phase 3 trials. The results are striking.
The Phase 2 trial (published in the New England Journal of Medicine, June 2023) enrolled 338 adults with obesity or overweight and tested multiple doses over 48 weeks:
| Dose | Weight Loss at 48 Weeks | Notes |
|---|---|---|
| Placebo | -2.1% | Control group |
| 1 mg | -8.7% | Lowest dose |
| 4 mg | -17.1% | Comparable to semaglutide 2.4mg |
| 8 mg | -22.8% | Comparable to tirzepatide 15mg |
| 12 mg | -24.2% | Exceeded all existing GLP-1 results |
At the 12mg dose, the responder rates were remarkable: 100% of participants achieved at least 5% weight loss, 93% achieved 10%+, 83% achieved 15%+, and 26% lost more than 30% of their body weight.
Then in December 2025, Eli Lilly reported the first Phase 3 results from TRIUMPH-4 (445 participants with obesity and knee osteoarthritis, 68 weeks):
| Arm | Weight Loss | Absolute Loss |
|---|---|---|
| Retatrutide 12mg | -28.7% | ~71 lbs (32.3 kg) average |
| Retatrutide 9mg | -26.4% | ~64 lbs (29.1 kg) average |
| Placebo | -2.1% | — |
How It Compares to Current GLP-1s
| Drug | Receptors | Max Weight Loss | Trial Duration | Status |
|---|---|---|---|---|
| Semaglutide (Wegovy) | GLP-1 | ~15-17% | 68 weeks | FDA approved (2021) |
| Tirzepatide (Zepbound) | GLP-1 + GIP | ~22-26% | 72 weeks | FDA approved (2023) |
| Retatrutide | GLP-1 + GIP + Glucagon | ~24-29% | 48-68 weeks | Phase 3 trials (not approved) |
Early body composition data suggests retatrutide may also have favorable effects on fat vs. muscle loss. In available analyses, fat mass accounted for approximately 67% of total weight lost with retatrutide, compared to about 61% with semaglutide. Tirzepatide showed the best fat-to-lean ratio at roughly 75% fat loss. These are preliminary comparisons across different trials, not head-to-head data.
Side Effects: What the Trials Show
The side effect profile is similar to existing GLP-1s, with one notable new signal:
| Side Effect | Retatrutide 12mg | Context |
|---|---|---|
| Nausea | Up to 43% | Similar to Wegovy (44%) |
| Diarrhea | ~33% | Slightly higher than Wegovy (30%) |
| Constipation | ~25% | Comparable to Wegovy (24%) |
| Vomiting | ~21% | Similar to Wegovy (25%) |
| Dysesthesia (tingling/burning skin) | 20.9% at 12mg | NEW — not seen with other GLP-1s |
Discontinuation rates in TRIUMPH-4 were 18.2% at the 12mg dose, 12.2% at 9mg, and 4.0% for placebo. Most GI side effects were mild to moderate and improved within 8-12 weeks during dose escalation. Retatrutide did not increase serious adverse events versus placebo.
When Could Retatrutide Be Available?
- •Current status (April 2026): Phase 3 trials ongoing across the TRIUMPH program. NOT approved anywhere globally.
- •TRIUMPH-4 results reported December 2025 — first Phase 3 readout. Seven additional Phase 3 readouts expected throughout 2026.
- •NDA submission to FDA: Expected Q4 2026 or Q1 2027, per Eli Lilly's Q4 2025 earnings call (February 2026).
- •FDA review: Standard review takes 10 months. Priority Review could shorten to 6 months.
- •Potential FDA approval: Late 2027 to early 2028.
- •Commercial launch: Estimated early 2028.
No brand name has been announced yet. Pricing is expected to be in the $1,000-1,500/month range at list price, similar to or slightly above current tirzepatide pricing, given its superior efficacy data.
What This Means for You
Retatrutide is not available yet, and won't be for at least 18-24 months. If you're considering GLP-1 treatment now, the currently approved options — semaglutide (Wegovy) and tirzepatide (Zepbound) — are effective and available today. There's no reason to wait for retatrutide if you qualify for treatment now.
However, if you're already on a GLP-1 and interested in what's next, retatrutide represents a significant step forward — particularly the addition of glucagon receptor agonism, which may enable greater fat loss with potentially less muscle loss. We'll update this article as new TRIUMPH trial results are published throughout 2026.
In the meantime, check our provider rankings to find the best GLP-1 program available today, or use our cost calculator to estimate what you'd pay with your insurance.
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting any medication. Information is current as of the publication date but may change.
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