Retatrutide Half-Life: What the Trial Data Shows and Does Not
Retatrutide's half-life was approximately 6 days in a phase 1b trial of 72 adults with type 2 diabetes, published in The Lancet in 2022. Retatrutide (LY3437943) is an investigational GIP, GLP-1, and glucagon receptor agonist from Eli Lilly. It is not FDA approved, so there is no drug label, only trial data.[1]
Retatrutide half-life calculator
Estimate, not a lab result. Levels are relative: each dose is scaled so its own peak equals its mg. The shaded band is a sensitivity range, not a confidence interval.
What is the half-life of retatrutide?
In the phase 1b trial published in The Lancet in 2022, the pharmacokinetics of retatrutide, then called LY3437943, were dose proportional and its half-life was approximately 6 days.[1] Half-life is the time for the amount of a drug in the body to fall by half. Dose proportional means that doubling the dose roughly doubled the exposure, so the half-life did not depend on how much was given. Six days sits between tirzepatide at about 5 days and semaglutide at about 1 week, both taken from their FDA labels.[5][6] The figure is a single approximate value from an early study in people with type 2 diabetes. It is not a label statement, and the abstract gives no interval around it. The calculator above is preset to 6 days, which is 144 hours. Treat it as a reasonable working number, not a settled measurement for every person.
Where does the 6-day figure come from?
It comes from a phase 1b, multicenter, double-blind, placebo-controlled, randomized, multiple-ascending-dose trial led by Eli Lilly authors and published in The Lancet in 2022.[1] Seventy-two adults enrolled and received at least one dose: 15 received placebo, 5 received dulaglutide, and 52 received retatrutide.[1] Participants were aged 20 to 70 and had type 2 diabetes. The study period was 12 weeks, and dose cohorts stepped up from 0.5 mg to 3, 6, 9, and 12 mg.[1] Eli Lilly and Company funded it. Participants were randomized to retatrutide, placebo, or dulaglutide, so half-life was one measurement among several in the study. The abstract reports one approximate half-life for the program, not a spread of values across participants. Nothing in it shows how the figure varies by age, weight, or health condition, so it should not be read as a fixed property for every person.
| Source | Population | Size | Length | Half-life reported |
|---|---|---|---|---|
| Phase 1b, The Lancet 2022[1] | Adults 20 to 70 with type 2 diabetes | 72 (52 on retatrutide) | 12 weeks | approximately 6 days |
| Phase 2, NEJM 2023[2] | Adults with obesity, or overweight with a weight-related condition | 338 | 48 weeks | none in the abstract |
| FDA drug label[3] | Not applicable | Not applicable | Not applicable | none: not an approved drug |
What is not yet known about retatrutide's pharmacokinetics?
Several things are not established in published label data, because no label exists. There is no FDA prescribing information, so there is no officially reviewed statement of half-life, time to peak, or steady state.[3] The one published half-life is an approximate value from a trial of adults with type 2 diabetes, and the abstract gives no interval around it.[1] The larger phase 2 trial in people with obesity reported weight outcomes over 48 weeks, and its abstract does not mention a half-life.[2] This page therefore cannot say how the half-life differs in people with kidney or liver problems, older adults, or other groups. It also cannot say what the time to peak is. The calculator above assumes a peak about 24 hours after a dose. That is a modeling choice, not a trial result. Anyone reading a single precise number for retatrutide is reading more precision than the evidence supports.
Is retatrutide FDA approved?
No. Retatrutide is an investigational drug, and the FDA states that retatrutide and cagrilintide cannot be used in compounding under federal law.[3] The agency also says they are not components of FDA-approved drugs and have not been found safe and effective for any condition.[3] The FDA has warned companies that illegally sold unapproved drugs containing retatrutide and similar compounds that are falsely labeled for research purposes or not for human consumption, noting that such products were sold directly to consumers for human use with dosing instructions.[3] The FDA page was current as of October 1, 2026 when it was checked for this article. In plain terms, there is no prescription retatrutide product and no lawful compounded version. PepTrac does not sell or supply retatrutide or any peptide. It is a record-keeping app, and its modeled curve is an educational estimate, not medical advice.
How does retatrutide's half-life compare with semaglutide and tirzepatide?
At about 6 days, retatrutide's half-life sits between tirzepatide's roughly 5 days and semaglutide's roughly 1 week.[1][5][6] On a weekly schedule, simple math puts the share left after 7 days at 44.5 percent for retatrutide, against 37.9 percent for tirzepatide and 50 percent for semaglutide. Five half-lives take about 30 days for retatrutide, 25 days for tirzepatide, and 35 days for semaglutide. Retatrutide also differs in mechanism. Tirzepatide acts on GIP and GLP-1 receptors,[6] while retatrutide adds the glucagon receptor, as its published trial title says.[1] The comparison is only as strong as its weakest number. Two of the three values come from FDA labels, while retatrutide's comes from one early trial, so the table below should be read as a rough guide to the order of magnitude. Half-life also says nothing about how well any of these drugs works.
| Drug | Half-life | FDA status | Share left at day 7 | Five half-lives | Build-up ratio |
|---|---|---|---|---|---|
| Semaglutide | about 1 week[5] | Approved (Ozempic, Wegovy) | 50% | 35 days | 2.00 |
| Tirzepatide | about 5 days[6] | Approved (Mounjaro, Zepbound) | 37.9% | 25 days | 1.61 |
| Retatrutide | about 6 days[1] | Investigational, not approved[3] | 44.5% | 30 days | 1.80 |
How long would retatrutide take to reach steady state?
If the 6-day half-life holds, the general rule gives an answer, but it is a calculation and not a trial result. Pharmacokinetic literature describes steady state as taking about five half-lives of repeated dosing,[4] which for 6 days is roughly 24 to 30 days, or four to five weekly doses. PepTrac's model agrees. With weekly 1 mg doses, the modeled level just before the next dose is 0.90 after the fourth dose and 0.92 after the fifth, against a plateau of about 0.93, with a range of 0.66 to 1.20 at the plateau. The model's peak at the plateau is about 1.84. These values are relative to one dose's own peak and are not blood concentrations. A missed weekly dose lowers the level a week later from about 0.93 to about 0.41, with a range of 0.24 to 0.61. That is a model of concentration, not guidance on missed doses.
| Doses taken | Level before next dose | Share of plateau |
|---|---|---|
| 1 | 0.52 | 56% |
| 2 | 0.75 | 81% |
| 3 | 0.85 | 91% |
| 4 | 0.90 | 97% |
| 5 | 0.92 | 99% |
| 12 | 0.93 (range 0.66 to 1.21) | 100% |
How does PepTrac model a compound with trial-only data?
PepTrac uses the same method for every compound, and it labels what the number rests on. For retatrutide it takes the 144 hour half-life from the published trial and an assumed time to peak of 24 hours, then draws a one-compartment absorption curve.[1] Each dose is scaled so that its own peak equals its milligrams, because the app cannot know an individual's blood concentration. The result is shown with a range. PepTrac varies the half-life and the time to peak by 20 percent in each direction, runs all nine combinations, and shades the lowest and highest result. That is a sensitivity range and not a statistical confidence interval. For one 1 mg dose, the modeled level at day 7 is 0.52 with a range of 0.42 to 0.59, and at day 14 it is 0.23, range 0.15 to 0.30. PepTrac tracks and estimates. It does not supply, sell, or recommend any peptide.
Frequently asked questions
Is retatrutide available by prescription?
No. Retatrutide is investigational and not FDA approved, and the FDA says it cannot be used in compounding under federal law. No lawful prescription product exists. Be cautious of anything sold online as retatrutide.
Is the 6-day half-life confirmed in larger trials?
The 6-day figure comes from the phase 1b trial in 72 adults with type 2 diabetes. The 338-person phase 2 obesity trial reported weight outcomes, and its abstract does not give a half-life, so this page cannot call it confirmed.
Why does PepTrac show a range for retatrutide?
PepTrac uses the same 20 percent sweep for every compound. Early, single-trial data is one more reason not to print one precise number. The shaded band is a sensitivity range, not a statistical confidence interval.
Can I track retatrutide in PepTrac?
PepTrac is a record-keeping app, and it lists retatrutide with the source for its half-life. It does not sell, supply, prescribe, or recommend it. Check your own legal and medical situation with a clinician.
Is retatrutide the same as tirzepatide?
No. Tirzepatide targets the GIP and GLP-1 receptors, and it is FDA approved as Mounjaro and Zepbound. Retatrutide also targets the glucagon receptor, and it is still in clinical trials.
When might retatrutide be approved?
No approval date is established in the sources checked for this page, so none is given. Approval depends on the FDA reviewing completed trials. Check the FDA and Eli Lilly for current news instead of relying on predictions.
Sources
- The Lancet (via PubMed, National Library of Medicine). LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Accessed October 3, 2026.
- New England Journal of Medicine (via PubMed, National Library of Medicine). Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. Accessed October 3, 2026.
- U.S. Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. Accessed October 3, 2026.
- Drug Design, Development and Therapy (via PubMed Central). Contribution of Trough Concentration Data in the Evaluation of Multiple-Dose Pharmacokinetics for Drugs with Delayed Distributional Equilibrium and Long Half-Life. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Novo Nordisk). Ozempic (semaglutide) injection prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Eli Lilly). Mounjaro (tirzepatide) injection prescribing information. Accessed October 3, 2026.
Written and maintained by the team that builds PepTrac. Every calculator on this site runs the same tested math as the app. Read how we research, cite, and update pages in our editorial policy.
