Retatrutide (LY3437943) is an investigational once-weekly injectable from Eli Lilly that activates three metabolic receptors at once — GLP-1, GIP, and glucagon. It is not FDA approved as of May 2026 and is available only through clinical trials.
Its glucagon component is the differentiator: on top of the appetite suppression shared with semaglutide and tirzepatide, glucagon agonism raises energy expenditure and hepatic fat oxidation — which appears to push weight loss and liver-fat reduction beyond the current generation of drugs.
Efficacy has been exceptional: 24.2% mean weight loss at 48 weeks in Phase 2, and up to 28.7% at 68 weeks in the first Phase 3 readout (TRIUMPH-4) — the largest ever reported in an obesity trial. Side effects are mostly gastrointestinal, plus a newly observed, dose-dependent skin-sensation signal (dysesthesia) that is being watched closely.
→ Estimate drug levels over a weekly cycle with the Half-Life Visualizer, or compare it head-to-head against tirzepatide and semaglutide in the Comparison Tool.
On this page
- What is retatrutide?
- Is retatrutide FDA approved? Status & timeline
- How it works: the triple-agonist mechanism
- Clinical evidence: every trial so far
- Weight-loss results at a glance
- Dosing & titration (from the trials)
- Side effects & safety
- Retatrutide vs other GLP-1 drugs
- Beyond weight loss: other indications
- Cost, access & legality
- Frequently asked questions
- Related on Grey Peptides
- Sources
What is retatrutide?
Retatrutide is an investigational drug being developed by Eli Lilly for chronic weight management and type 2 diabetes. Chemically it is a single synthetic peptide — a 39-amino-acid chain attached to a long fatty-acid tail that extends its half-life to roughly six days, enabling once-weekly subcutaneous injection. It is frequently referred to by its development code, LY3437943, or by the nickname "Triple-G."
What makes it notable is that one molecule simultaneously activates three different hormone receptors. The current best-in-class drug, tirzepatide, activates two (GLP-1 and GIP). Semaglutide activates one (GLP-1). Retatrutide is the first triple agonist to reach Phase 3 trials, adding glucagon-receptor activation to the mix. That third lever is the reason it is being studied not only for obesity and diabetes but for fatty-liver disease, knee osteoarthritis, sleep apnea, and cardio-renal conditions.
Crucially, retatrutide has not completed its clinical program. It is not approved, not prescribable for weight loss, and the long-term safety picture is still being assembled. Everything below reflects trial data and regulatory filings, not a product you can buy.
Is retatrutide FDA approved? Status & timeline
No. Retatrutide is not FDA approved — and not approved by the EMA or any other regulator — as of May 2026. It remains an investigational compound in late-stage testing. This is the single most common question about the drug, so to be unambiguous: it cannot currently be lawfully prescribed or sold as a medicine for obesity or diabetes.
Lilly's Phase 3 program is called TRIUMPH, and it spans more than 5,800 participants across obesity, type 2 diabetes, osteoarthritis, sleep apnea, chronic low-back pain, fatty-liver disease, and cardio-renal outcomes. The first readout, TRIUMPH-4, reported in December 2025. Seven additional Phase 3 readouts are expected through 2026. A New Drug Application is widely anticipated around late 2026 once the full data package is assembled, which would put a realistic approval decision in the 2027–2028 window. None of these dates are confirmed by Lilly or the FDA; drug timelines slip routinely.
| Milestone | Status |
|---|---|
| Phase 2 obesity & T2D results (NEJM, Lancet) | ✅ Published 2023 |
| Phase 2 MASLD liver-fat substudy (Nature Medicine) | ✅ Published 2024 |
| TRIUMPH-4 — first Phase 3 readout (obesity + knee OA) | ✅ Topline Dec 2025 |
| TRANSCEND-T2D-1 — Phase 3 in type 2 diabetes | ✅ Topline March 2026 |
| Remaining TRIUMPH Phase 3 readouts | ⏳ Expected through 2026 |
| FDA submission (NDA) | ⏳ Anticipated ~late 2026 (not confirmed) |
| Possible FDA decision | ⏳ Estimated 2027–2028 (not confirmed) |
For context on how fast this category is now moving, Lilly's oral GLP-1 pill orforglipron (Foundayo) went from filing to the fastest new-molecular-entity approval since 2002 — see our news coverage of the orforglipron approval. Retatrutide is the higher-efficacy injectable following behind it.
→ Full detail, including a stage-by-stage timeline: Is retatrutide FDA approved? Status & timeline.
How it works: the triple-agonist mechanism
Retatrutide's effects come from activating three receptors that each pull a different metabolic lever. The first two are familiar from existing drugs; the third is what sets it apart.
GLP-1 receptor — appetite & satiety. Like semaglutide, retatrutide mimics GLP-1 to reduce hunger, quiet "food noise," slow gastric emptying, and improve glucose-dependent insulin release. This is the backbone of every drug in this class.
GIP receptor — metabolic amplifier. Like tirzepatide, it also activates GIP, which appears to improve how fat tissue handles insulin and may soften the nausea that pure GLP-1 agonism can cause. Notably, in laboratory potency terms retatrutide is most potent at the GIP receptor.
Glucagon receptor — the new lever. This is the mechanistic differentiator. Glucagon is best known for raising blood sugar, but at the liver and in fat tissue it also increases energy expenditure and drives fat oxidation. Adding controlled glucagon agonism means the body burns more energy and mobilizes liver fat, on top of eating less. The trade-off is that the glucagon component must be balanced carefully through dose titration so it does not work against the glucose-lowering benefits — which is why trial protocols escalate the dose slowly.
The practical upshot: appetite suppression (GLP-1) + metabolic efficiency (GIP) + increased energy burn and hepatic fat clearance (glucagon) combine into a larger total effect than either single- or dual-agonist drugs achieve. It also helps explain why liver fat and triglycerides dropped more than weight loss alone would predict in the trials below.
→ See the structured molecular profile, sequence, and pathway breakdown in the retatrutide encyclopedia entry.
Clinical evidence: every trial so far
Retatrutide has one of the most closely watched data sets in metabolic medicine. Here is what each major study has shown.
Phase 2 obesity trial (NEJM, 2023)
The landmark Phase 2 trial in adults with obesity but without diabetes tested 1, 4, 8, and 12 mg weekly doses over 48 weeks. Weight loss was strongly dose-dependent: roughly 17.1% at 4 mg, 22.8% at 8 mg, and 24.2% at 12 mg — at the time the largest figure reported for any drug in the GLP-1 class. About 93% of participants on 12 mg lost at least 15% of body weight, and effectively all lost at least 5%. Beyond the scale, the trial showed improvements in blood pressure, lipids, and blood sugar; 72% of participants who had prediabetes at baseline returned to normal glucose levels, and a meaningful share of people on the higher doses were able to stop at least one blood-pressure medication.
Phase 2 type 2 diabetes trial (Lancet, 2023)
A parallel Phase 2 trial in people with type 2 diabetes showed about 16.9% weight loss at 36 weeks, alongside an HbA1c reduction of roughly 2.2 percentage points, with the large majority of participants reaching an HbA1c at or below 6.5%. This established that the triple-agonist approach controls blood sugar as well as it drives weight loss.
Phase 2 liver-fat (MASLD) substudy (Nature Medicine, 2024)
A substudy of the obesity trial looked at people who also had fatty-liver disease (MASLD) with significant baseline liver fat. The reductions in liver fat were striking and dose-dependent — on the order of 81–82% at the 8 mg and 12 mg doses by 24 weeks, versus essentially no change on placebo. At the higher doses, a large majority of participants achieved normal liver-fat levels, and hepatic steatosis resolved in more than 85% of them. The liver-fat drop outpaced the weight loss, which researchers attribute to the glucagon component acting directly on the liver.
TRIUMPH-4 — first Phase 3 readout (December 2025)
TRIUMPH-4 was the first Phase 3 trial to report. It enrolled 445 adults with overweight or obesity and knee osteoarthritis (no diabetes), randomized to 9 mg, 12 mg, or placebo for 68 weeks. From an average starting weight around 248 lbs (BMI ~40), the 12 mg dose produced up to 28.7% mean weight loss (about 71 lbs), versus roughly 2% on placebo — the largest weight reduction reported in any obesity trial to date. Both doses met all primary and key secondary endpoints, and also delivered clinically meaningful reductions in knee-osteoarthritis pain and improvements in physical function, plus reductions in cardiovascular risk markers such as non-HDL cholesterol and systolic blood pressure. Full results are slated for a future medical meeting and peer-reviewed publication.
TRANSCEND-T2D-1 — Phase 3 in diabetes (March 2026)
Lilly reported topline Phase 3 results in type 2 diabetes in March 2026, extending the diabetes evidence base into the registrational program. Detailed data are pending publication. The remaining TRIUMPH and TRANSCEND readouts — covering obesity, diabetes, sleep apnea, and cardio-renal outcomes — are expected through 2026 and will determine the breadth of any eventual label.
Weight-loss results at a glance
| Trial | Population | Dose | Duration | Mean weight loss |
|---|---|---|---|---|
| Phase 2 (NEJM) | Obesity, no T2D | 4 mg | 48 wks | ~17.1% |
| Phase 2 (NEJM) | Obesity, no T2D | 8 mg | 48 wks | ~22.8% |
| Phase 2 (NEJM) | Obesity, no T2D | 12 mg | 48 wks | ~24.2% |
| Phase 2 (Lancet) | Type 2 diabetes | up to 12 mg | 36 wks | ~16.9% |
| TRIUMPH-4 (Phase 3) | Obesity + knee OA | 9 mg | 68 wks | (high; full data pending) |
| TRIUMPH-4 (Phase 3) | Obesity + knee OA | 12 mg | 68 wks | ~28.7% |
Figures are trial averages; individual results vary widely with dose, duration, and baseline weight. Weight is typically regained after stopping any drug in this class unless lifestyle change is sustained.
Dosing & titration (from the trials)
Retatrutide has no FDA-approved dose, label, or prescribing information because it is not approved for any use. The schedules below describe what was used in clinical trials under medical supervision and are provided for education and to interpret the research — not as instructions for use. Self-administration of unapproved drugs carries unknown and potentially serious risks.
Across the program, retatrutide is given as a once-weekly subcutaneous injection, with the dose escalated slowly to manage gastrointestinal side effects and to balance the glucagon component. The Phase 2 obesity trial used target doses of 1, 4, 8, and 12 mg, reaching the target through a stepped titration (for example, 2 → 4 → 8 → 12 mg over several months). TRIUMPH-4 evaluated the two highest doses, 9 mg and 12 mg. The maximum weight loss occurred at the 8–12 mg range; lower doses produced proportionally less effect.
Slow titration matters more here than with single-agonist drugs, because the glucagon receptor adds both efficacy and complexity. In TRIUMPH-4, some discontinuations were actually attributed to excessive or overly rapid weight loss in lower-BMI participants — a reminder that "more and faster" is not automatically better.
→ If you are studying reconstitution math or want to model concentration over a weekly cycle, the Reconstitution Calculator and Half-Life Visualizer are built for exactly that.
→ Full breakdown of every trial schedule and the dose-response curve: Retatrutide dosage guide.
Side effects & safety
The safety profile is broadly consistent with other incretin drugs, dominated by gastrointestinal effects that tend to be worst during dose escalation and ease over time. The one genuinely new finding from Phase 3 is a skin-sensation signal called dysesthesia.
Adverse events in TRIUMPH-4
| Adverse event | 9 mg | 12 mg | Placebo |
|---|---|---|---|
| Nausea | 38.1% | 43.2% | 10.7% |
| Diarrhea | 34.7% | 33.1% | 13.4% |
| Constipation | 21.8% | 25.0% | 8.7% |
| Vomiting | 20.4% | 20.9% | 0.0% |
| Decreased appetite | 19.0% | 18.2% | 9.4% |
| Dysesthesia | 8.8% | 20.9% | 0.7% |
| Discontinuation due to adverse events | 12.2% | 18.2% | 4.0% |
What is dysesthesia, and how concerned should we be?
Dysesthesia is an abnormal sense of touch — normal sensations (clothing, a light touch) can feel tingling, prickling, or uncomfortable. In TRIUMPH-4 it appeared in a clearly dose-dependent way and had not been flagged in the earlier Phase 2 work. The reported events were generally mild and rarely caused people to stop treatment, but it is a new signal that analysts and clinicians say they will be watching across the remaining Phase 3 readouts and in the full TRIUMPH-4 publication. It is one of the clearest reasons the complete safety picture won't be settled until the program finishes.
The bigger safety caveat
Because retatrutide is investigational, there is no long-term human safety record, no established contraindication list, and no post-marketing surveillance. Drugs in this class generally carry class warnings (for example, around thyroid C-cell tumors seen in rodent studies, pancreatitis risk, and gallbladder events), and final labeling — if approved — will define these formally. Until then, any use outside a trial is uncharted. Anyone considering a GLP-1-class drug should review interactions and contraindications with a clinician; our GLP-1 drug interactions guide covers the known territory for approved drugs in the family.
Retatrutide vs other GLP-1 drugs
Retatrutide sits at the leading edge of a fast-moving class. Here is how it lines up against the current and next-generation options.
| Drug | Receptors | Route | Peak trial weight loss | Status (2026) |
|---|---|---|---|---|
| Retatrutide | GLP-1 + GIP + glucagon (triple) | Weekly injection | ~28.7% (Ph3) | Investigational (Phase 3) |
| Tirzepatide | GLP-1 + GIP (dual) | Weekly injection | ~22.5% (SURMOUNT-1) | Approved (Mounjaro/Zepbound) |
| Semaglutide | GLP-1 (single) | Weekly injection / oral | ~14.9% (STEP 1) | Approved (Ozempic/Wegovy) |
| Survodutide | GLP-1 + glucagon (dual) | Weekly injection | ~19% (Ph2) | Investigational |
| CagriSema | GLP-1 + amylin (combo) | Weekly injection | ~22.7% (REDEFINE-1) | Investigational |
| Orforglipron | GLP-1 (single, oral non-peptide) | Daily pill | ~12.4% (ATTAIN-1) | Approved Apr 2026 (Foundayo) |
The short version: retatrutide currently holds the highest efficacy numbers thanks to its third (glucagon) receptor, but it is also the least mature on safety and the furthest from market of the injectables. Tirzepatide remains the approved efficacy leader you can actually get today.
→ For a deeper head-to-head on the two approved leaders, read Semaglutide vs Tirzepatide, or build your own multi-metric comparison in the Comparison Tool.
→ Full retatrutide-vs-tirzepatide breakdown: Retatrutide vs Tirzepatide.
Beyond weight loss: other indications
Because the glucagon lever produces effects that are partly independent of weight, the TRIUMPH program is testing retatrutide across a range of conditions:
- Knee osteoarthritis — TRIUMPH-4 showed meaningful pain reduction and improved physical function alongside weight loss.
- Type 2 diabetes — strong HbA1c reductions in Phase 2; Phase 3 (TRANSCEND-T2D-1) reported topline in early 2026.
- Fatty-liver disease (MASLD/MASH) — dramatic liver-fat reductions in the Phase 2 substudy, driven partly by direct hepatic effects.
- Obstructive sleep apnea — under evaluation in the Phase 3 program.
- Chronic low-back pain & cardio-renal outcomes — additional readouts expected through 2026.
If approved, the eventual label will depend on which of these trials succeed — so the breadth of retatrutide's future use is still being written.
Cost, access & legality
How much will it cost? No price exists yet because the drug isn't approved. Based on where tirzepatide and the broader class sit, analysts generally project a list price somewhere in the range of roughly $1,000–$1,500 per month at launch, before insurance or competitive pressure — but this is an estimate, not a quote.
How do people access it today? There is exactly one lawful route: enrolling in an active clinical trial, where the drug is provided under medical supervision at no cost. Retatrutide cannot be prescribed for obesity, and it sits on the FDA's restricted list for compounding, so compounding pharmacies are not a legal pathway either.
The grey market. Retatrutide is widely sold online as a "research chemical." These products are unregulated and not intended for human use; identity, purity, dose accuracy, and sterility are unverified, and buying or using them falls entirely outside any approved medical framework. The recent wave of vendor shutdowns and enforcement actions across the peptide market underscores how little buyer protection exists in that space. Grey Peptides does not sell products and does not link to vendors — our role is to document the science and the rules clearly so you can make informed decisions. For the regulatory backdrop, see Are Peptides Legal?
Frequently asked questions
Is retatrutide FDA approved?
No. As of May 2026 it is investigational and only available through clinical trials. The first Phase 3 readout (TRIUMPH-4) came in December 2025; an FDA submission is widely expected around late 2026, with a possible approval window in 2027–2028 — none of which is confirmed.
When will retatrutide be approved?
There is no confirmed date. The realistic earliest window most observers cite is 2027, possibly slipping to 2028, contingent on the remaining 2026 Phase 3 readouts and FDA review. Treat any specific "release date" you see online as speculation.
How much weight can you lose on retatrutide?
In trials, the 12 mg dose produced about 24.2% mean weight loss at 48 weeks (Phase 2) and up to 28.7% at 68 weeks (Phase 3 TRIUMPH-4). Those are averages; individual results vary, and weight tends to return after stopping any drug in this class.
How is it different from Ozempic or Mounjaro?
Ozempic (semaglutide) hits one receptor; Mounjaro/Zepbound (tirzepatide) hits two. Retatrutide adds a third — glucagon — which increases energy expenditure and liver-fat clearance on top of appetite suppression. That third lever is why its trial weight-loss numbers are higher.
What are the side effects?
Mostly gastrointestinal — nausea, diarrhea, constipation, vomiting, reduced appetite — typically worst during dose escalation. Phase 3 also surfaced a new, dose-dependent skin-sensation effect (dysesthesia) that was generally mild but is being monitored.
Is there an oral version of retatrutide?
No. Retatrutide is an injectable peptide. The oral option in Lilly's portfolio is orforglipron (a non-peptide GLP-1 pill, approved April 2026) — a different molecule with lower efficacy.
Can I get retatrutide from a compounding pharmacy?
No. It is not approved and is on the FDA's restricted list for compounding, so compounding is not a lawful route. The only legal access is a clinical trial.
Is retatrutide safe?
Its short-term trial profile resembles other incretin drugs, but because it is investigational there is no long-term human safety record and no approved labeling. The full safety picture won't be clear until the Phase 3 program finishes and is published.
Related on Grey Peptides
Encyclopedia entries
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Sources
Primary literature and regulatory/clinical reporting. Trial figures are topline unless a peer-reviewed publication is cited.
- Jastreboff AM, et al. "Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." N Engl J Med. 2023;389(6):514–526.
- Rosenstock J, et al. "Retatrutide in patients with type 2 diabetes — a Phase 2 trial." Lancet. 2023;402(10401):529–544.
- Sanyal AJ, et al. "Triple hormone receptor agonist retatrutide for MASLD: a randomized phase 2a trial." Nature Medicine. 2024.
- Eli Lilly & Company. TRIUMPH-4 Phase 3 topline results (obesity + knee osteoarthritis). News release, December 11, 2025.
- Eli Lilly & Company. TRANSCEND-T2D-1 Phase 3 topline (type 2 diabetes). Company communication, March 2026.
- ClinicalTrials.gov — TRIUMPH program (e.g., NCT05882045) and related Phase 3 registrations.
- U.S. FDA. Guidance and bulks-list determinations affecting peptide compounding (503A/503B), 2023–2026.
Medical disclaimer: This page is for education only and is not medical advice. Retatrutide is investigational and not approved for use. Do not start, stop, or self-administer any drug based on this page; consult a licensed clinician.