Retatrutide: Lilly's Triple-Agonist Weight Loss Drug
The first GLP-1 medication to add glucagon-receptor activation. Phase 3 trials nearing readout. Expected FDA decision late 2026 to early 2027.
Retatrutide is Eli Lilly's next-generation weight-loss injection, in late Phase 3 trials. It activates three gut and pancreatic receptors at once — GLP-1, GIP, and glucagon — and produced 24.2% body weight loss at 48 weeks in published Phase 2 data, the highest weight loss ever recorded for a non-bariatric obesity drug at the time. Lilly has guided to FDA submission in 2026, putting potential approval in late 2026 or first half of 2027. Retatrutide is not yet available through any legitimate pharmacy, including compounding pharmacies.
Retatrutide is an investigational drug. It cannot legally be prescribed, dispensed, or sold by any pharmacy in the United States. Vials sold online with a “research use only” label are unregulated and unsafe to inject. This page tracks the science and timeline. For a currently approved triple-class option, see Zepbound.
What is retatrutide?
Retatrutide is Eli Lilly's next major weight-loss injection. It is a once-weekly subcutaneous shot, the same delivery format as Wegovy, Ozempic, Mounjaro, and Zepbound. What sets it apart is the mechanism: retatrutide is the first medication in late-stage development to activate three different gut and pancreatic receptors at once.
That extra receptor matters. In the published Phase 2 trial, adults at the highest dose lost 24.2% of their body weight at 48 weeks — and the curve had not flattened. By comparison, tirzepatide reached 22.5% weight loss in its pivotal SURMOUNT-1 trial at 72 weeks. Same trial population, same primary endpoint, more weight lost in less time.
Lilly is also studying retatrutide for type 2 diabetes (TRIUMPH-2), cardiovascular outcomes (TRIUMPH-3), and metabolic dysfunction-associated steatohepatitis or MASH (TRIUMPH-4). The MASH program is the one to watch — Phase 2 showed the largest reductions in liver fat ever reported for a GLP-1 class drug.
The triple-agonist mechanism
Retatrutide activates three gut and pancreatic receptors at once: GLP-1 (the same target as Wegovy), GIP (the additional target Zepbound hits), and glucagon (a new target for the weight-loss class). The glucagon component is the key differentiator — it directly increases energy expenditure and recruits the liver to mobilize stored fat.
Zepbound (tirzepatide) is a dual agonist hitting GLP-1 and GIP. Retatrutide adds the glucagon receptor on top of those two, which appears to translate into greater weight loss in head-to-head Phase 2 data and more pronounced improvements in liver fat.
Wegovy (semaglutide) is a single agonist hitting only GLP-1. Retatrutide's three-receptor mechanism produced roughly twice the percent weight loss of semaglutide in comparable trial populations and durations.
The Phase 2 result that started the wait
In August 2023, the New England Journal of Medicine published the Phase 2 results for retatrutide. 338 adults with obesity were randomized to placebo or one of four retatrutide doses for 48 weeks. The headline number — 24.2% mean body weight reduction at 12 mg — was the largest weight loss ever recorded for a non-bariatric obesity drug at the time of publication.
| Dose | Mean weight loss at 48 weeks |
|---|---|
| 1 mg weekly | 8.7% |
| 4 mg weekly | 17.1% |
| 8 mg weekly | 22.8% |
| 12 mg weekly | 24.2% |
Key detail: Critically, weight loss had not plateaued by week 48 in the 8 mg and 12 mg arms. Phase 3 trials run longer to test where the curve flattens.
Side effects: Predominantly gastrointestinal — nausea, diarrhea, vomiting, constipation. Most were mild to moderate and dose-dependent. Glucagon receptor activation produced a transient increase in heart rate (about 6 bpm at the highest dose) that warrants longer monitoring in Phase 3.
Source: Jastreboff AM et al., “Triple–Hormone-Receptor Agonist Retatrutide for Obesity,” NEJM, August 2023.
Phase 3 trials in progress
Lilly is running four parallel Phase 3 programs under the TRIUMPH banner. Together they will determine whether retatrutide reaches the market and how broadly it will be indicated.
TRIUMPH-1
NCT05882045- Population
- Adults with obesity (no diabetes)
- Primary endpoint
- Percent change in body weight at 80 weeks
- Status
- Enrollment complete; readout expected 2026
TRIUMPH-2
NCT05929066- Population
- Adults with obesity and type 2 diabetes
- Primary endpoint
- Body weight and HbA1c reduction at 80 weeks
- Status
- Enrollment complete; readout expected 2026
TRIUMPH-3
NCT05882110- Population
- Adults with obesity and established cardiovascular disease
- Primary endpoint
- Major adverse cardiovascular events (MACE)
- Status
- Long-running outcomes trial; readout expected 2027 or later
TRIUMPH-4 (MASH program)
NCT05989711- Population
- Adults with obesity and metabolic dysfunction-associated steatohepatitis (MASH)
- Primary endpoint
- MASH resolution and fibrosis improvement on biopsy
- Status
- Active. Liver-fat improvements were the most striking secondary signal in the Phase 2 trial.
FDA & launch timeline
Lilly has guided to NDA filing in 2026 for the obesity indication, with the cardiovascular outcomes trial (TRIUMPH-3) reading out separately. Late 2026 to early 2027 for the obesity indication, contingent on FDA review timeline. Cardiovascular outcomes data may follow.
Launch window: Within 6 months of approval — Lilly's pattern with Mounjaro and Zepbound was rapid commercial launch following approval.
What could push it later: Additional safety data requests from FDA, supply scale-up constraints, or differentiation questions from regulators given Zepbound is already on market.
Anticipated pricing
No price has been set. The numbers below are projections based on how Lilly priced Mounjaro and Zepbound at launch. Treat as scenarios, not facts.
- Lilly's pricing pattern
- Mounjaro launched at $1,023 monthly list. Zepbound launched at $1,059 list, with cash-pay options that have come down over time (currently $299–$449/month via the LillyDirect Multi-Dose KwikPen).
- Expected list price
- $1,000 to $1,200 per month at launch
- Expected cash-pay floor
- Lilly will likely launch with a self-pay option similar to LillyDirect — anticipate $400–$600/month at the lowest doses initially, falling over the first 12–18 months as supply scales.
- Expected savings card
- If precedent holds, a Lilly Savings Card for commercially insured patients should bring monthly cost to around $25–$50/month at retail pharmacies, excluding federal plans.
- Policy context
- The Most-Favored-Nation pricing framework announced November 2025 may compress launch pricing. Medicare Part D coverage of GLP-1s for obesity begins July 2026 and will likely include retatrutide soon after approval.
Wait for retatrutide, or start tirzepatide now?
If you qualify for tirzepatide today, starting now is usually the right call. Retatrutide is months to years from broad availability. Tirzepatide (Zepbound) is already producing 20%+ body weight loss at the 15 mg dose and is widely accessible at $299–$449/month cash-pay. Switching to retatrutide later, if it offers meaningfully better outcomes for you, will be straightforward — these drugs are titrated similarly.
Exceptions: If you have advanced fatty liver disease (MASH/NAFLD) where the glucagon-receptor activation may matter clinically, the calculation is different. Discuss with a hepatologist. The TRIUMPH-4 program may make retatrutide the first GLP-1 with a specific MASH indication.
Do not buy retatrutide from research-use-only websites or unlicensed compounding pharmacies. The drug is not FDA-approved, the supply chain is unregulated, and the dosing flexibility argument that applies to compounded tirzepatide does not apply here — there is no on-label dosing to anchor against.
Recent milestones
Phase 2 results published in NEJM
2023-08-10Jastreboff et al. report 24.2% weight loss at 48 weeks at 12 mg, the highest weight loss ever reported for a non-bariatric obesity drug at that time.
TRIUMPH Phase 3 program fully enrolled
2024-Q3All four pivotal trials (obesity, T2D, cardiovascular, MASH) completed enrollment ahead of schedule.
Lilly reaffirms 2026 NDA filing target
2026-Q1On Q1 2026 earnings, Lilly leadership reiterated retatrutide remains on track for FDA submission within 2026.
Expected FDA approval window for obesity indication
2026-2027 (projected)Standard FDA review of a priority NDA from a major manufacturer with strong Phase 3 data typically runs 10 to 12 months. Earliest possible approval is late 2026; more likely first half of 2027.
Frequently asked
Keep reading
Retatrutide is not FDA-approved. Every claim on this page is sourced to one of: peer-reviewed publication (Phase 2 results in NEJM), ClinicalTrials.gov registry data (Phase 3 design and status), Lilly investor and pipeline disclosures (timeline guidance), or clearly labeled projection (anticipated pricing). We do not publish dosing instructions for unapproved drugs. We do not link to research-use-only suppliers. Medical content reviewed by Dr. Golsa Gholampour, MD, board-certified in obesity medicine. Page re-verified monthly until FDA submission status changes.