What retatrutide is
Retatrutide is a single peptide that acts on three hormone receptors, the ones for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1) and glucagon. It was studied under the code LY3437943. A 2022 paper in Cell Metabolism calls LY3437943 a novel triple agonist peptide. The paper's declaration says all its authors are employees and stockholders of Eli Lilly, and that one of them is a former employee.
A trial report published online by The Lancet in September 2026 says retatrutide is currently under investigation for the treatment of obesity, type 2 diabetes and other comorbidities, including knee osteoarthritis and obstructive sleep apnoea.
Where it stands with the FDA
Retatrutide isn't approved by the FDA. The agency's page on unapproved GLP-1 drugs, current as of October 1, 2026, says retatrutide isn't a component of any FDA-approved drug and hasn't been found safe and effective for any condition.
The same page says retatrutide can't be used in compounding under federal law. It says the agency has warned telehealth companies for marketing unapproved drugs such as retatrutide, distributors of active pharmaceutical ingredients for selling retatrutide and other GLP-1 drugs to compounders, and outsourcing facilities for repackaging it. FDA's list of substances nominated for compounding under section 503A, as updated May 14, 2026, was searched for retatrutide by name and by its code, and it isn't on it.
FDA also says it has warned companies that illegally sold unapproved drugs containing retatrutide, among other drugs, falsely labeled "for research purposes" or "not for human consumption". It says these products have been sold directly to consumers for human use with dosing instructions, that they're of unknown quality and may be harmful, and it urges consumers not to purchase them.
With no approved product there's no label. None of the documents this page rests on describes a retatrutide vial, its strength or how to mix it. The vial and water boxes on this page start empty for that reason, so enter what your own vial says.
What the trials tested
This section reports what published trials gave their participants. It's a record of what was studied and not a suggestion. None of the abstracts says how the trial product was supplied or mixed. All five abstracts name Eli Lilly as the funder.
A phase 1b trial published in The Lancet in 2022 gave people with type 2 diabetes once-weekly injections under the skin over a 12-week period. Its abstract says the top doses in the two highest dose cohorts were attained through stepwise dose escalations.
A phase 2 trial published in the New England Journal of Medicine in 2023 enrolled 338 adults who had a body-mass index of 30 or higher, or of 27 to less than 30 plus at least one weight-related condition. It tested retatrutide under the skin once weekly for 48 weeks, against placebo. One group received 1 mg. Two groups received 4 mg, one with an initial dose of 2 mg and one with an initial dose of 4 mg. Two groups received 8 mg, one with an initial dose of 2 mg and one with an initial dose of 4 mg. One group received 12 mg, with an initial dose of 2 mg. The abstract says the most common adverse events in the retatrutide groups were gastrointestinal, were dose-related and were mostly mild to moderate in severity. It also reports dose-dependent increases in heart rate that peaked at 24 weeks and declined thereafter.
A phase 3 trial called TRIUMPH-1, published online by the New England Journal of Medicine in September 2026, assigned adults with obesity and without diabetes to a once-weekly injection under the skin of retatrutide at 4 mg, 9 mg or 12 mg, or of placebo, for 80 weeks. A total of 2,339 participants underwent randomization. The abstract says the most common adverse events were gastrointestinal.
A phase 3 trial called TRIUMPH-2, published online by The Lancet in September 2026, enrolled adults with a body-mass index of 27 or higher and type 2 diabetes. It assigned 1,152 participants to once-weekly injections under the skin, given by the participants themselves, of retatrutide 4 mg, 9 mg or 12 mg, or of placebo. Its primary endpoint was measured at week 80. The abstract says the most frequently reported adverse events were gastrointestinal and were more common in the retatrutide groups than in the placebo group. It says hypotension and dysesthesia were more frequent with retatrutide than with placebo, and that permanently stopping treatment because of adverse events or death was more frequent at 9 mg and 12 mg than at 4 mg or on placebo. It reports that two participants died in the 4 mg group, three in the 9 mg group, one in the 12 mg group and one in the placebo group, and says the investigator deemed all of the deaths unrelated to the study intervention.
A 40-week phase 3 trial called TRANSCEND-T2D-1, published in The Lancet in 2026, tested retatrutide as a monotherapy in adults with type 2 diabetes that was inadequately controlled by diet and exercise alone. It assigned 537 participants to retatrutide at 4 mg, 9 mg or 12 mg, or to placebo, by once-weekly injection under the skin. The abstract says the most frequent adverse events with retatrutide were generally mild to moderate gastrointestinal events, which subsided over time. It says the share who stopped the study intervention because of adverse events was 2 to 5% with retatrutide and 0% with placebo. It reports two deaths, both in the 4 mg group, and calls them unrelated to the study drug.
None of the three phase 3 abstracts says whether the amount was stepped up over time to reach 4 mg, 9 mg or 12 mg, or how.
Storing retatrutide
None of the documents this page rests on gives storage conditions for retatrutide by name, either as a powder or after mixing. FDA's page on unapproved GLP-1 drugs says injectable GLP-1 drugs require refrigeration as indicated in their package inserts, and recommends not using any injectable GLP-1 drug that arrives warm or with insufficient refrigeration. Retatrutide has no approved product, so it has no package insert to check.
The same page makes a general point about vials that hold several doses of a sterile medication, in a passage about compounded GLP-1 medications. It says that, generally, FDA recommends such vials be used within 28 days after the first use, because the risk of contamination goes up after 28 days. It recommends discarding the vial within 28 days after the first use even if medication remains in it, and always using a new, sterile needle and syringe for each dose. That's about contamination. It doesn't say how long retatrutide itself stays stable.
There's no approved label for retatrutide, so nothing official says how long a mixed vial keeps.
Retatrutide dosage calculator questions
How do I turn a retatrutide dose into syringe units?
Divide the dose by the concentration to get millilitres, then multiply by 100. A 5 mg vial mixed with 2 mL is 2.5 mg/mL, so one unit on an insulin syringe holds 25 mcg and ten units hold 250 mcg.
How much bacteriostatic water goes in a 5 mg vial of retatrutide?
There's no single right amount. The water only sets the concentration, and the amount of retatrutide in the vial stays the same. With 5 mg, 1 mL makes 5 mg/mL, 2 mL makes 2.5 mg/mL and 3 mL makes 1.667 mg/mL. Choose the amount that puts your dose somewhere between about 10 and 40 units, where it's easiest to read.
Is retatrutide approved by the FDA?
No. FDA says retatrutide isn't a component of any FDA-approved drug, hasn't been found safe and effective for any condition, and can't be used in compounding under federal law. That's from an FDA page current as of October 1, 2026.
Does this page tell me how much retatrutide to take?
No. There's no FDA-approved retatrutide product, so there's no approved dose to point to. The page reports the amounts that published trials tested, as a record of what was studied and not as a suggestion. The dose box starts empty for that reason, and the chart only converts.
More peptide calculators by name
The same instrument, set up one peptide at a time. For any other vial, use the peptide reconstitution calculator.