Retatrutide half-life and steady state
6.3 days (estimated) modelled half-life, peaking 24 h after a dose. What that means for how long it lasts, how much it builds up, and when bloodwork is worth drawing.
- Also known as
- LY3437943, triple G agonist
- Class
- Metabolic Peptides
- Modelled half-life
- 6.3 days — estimated half-life, limited human PK data
- Time to peak
- 24 h
- Formulation
- Aqueous (reconstituted powder)
- Cleared per dosing interval
- 54% gone, 46% still present after 7 days
- Time to steady state
- ~31.3 days (about five half-lives)
- Accumulation at that cadence
- 1.85× a single dose
- Peak-to-trough at steady state
- 1.92×
- Regulatory status
- Phase III clinical trials ongoing as of 2026. Not FDA approved. Expect approval 2025-2026.
- Monitoring panel
- HbA1c, fasting glucose, lipids, liver enzymes, body composition monthly, weight weekly.
- Before mixing
- Sealed powder tolerates room temperature in transit, but keep it refrigerated at 2–8 °C (36–46 °F) for anything beyond a few weeks, or frozen for months. Keep it dark — the carton it shipped in is doing a job.
- After mixing
- Once reconstituted with bacteriostatic water: refrigerate at 2–8 °C and use within about 28 days. The benzyl alcohol in bacteriostatic water is what buys that window — plain sterile water has no preservative, so a vial mixed with it should be treated as one sitting only. Kits are usually ten vials: only the one you mixed is on that 28-day clock — the sealed ones keep their own, much longer shelf life, so store them as powder, not as solution.
- What ruins it
- Do not freeze a reconstituted vial. Repeated freeze–thaw is one of the more reliable ways to degrade a peptide.
- Handling caveat
- General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
Retatrutide's half-life figure carries a caveat the others on this site do not: it is an estimate. The app flags it as such, and the flag is not decoration. As of September 2026 retatrutide is an investigational compound in phase III trials; the public pharmacokinetic record is thin, and a figure of about six days is inferred from trial dosing intervals and the compound's design rather than read off a published human PK study. Every number on this page inherits that uncertainty.
What is reasonably solid is the shape. Retatrutide is a triple agonist — GIP, GLP-1 and glucagon — built with the same albumin-binding strategy as semaglutide and tirzepatide, and it was dosed weekly in trials, which only works for a molecule with a multi-day half-life. On that basis it accumulates for roughly a month before plateauing, like its predecessors, and produces a similarly flat week-to-week curve.
The glucagon arm is what makes the long half-life worth thinking about rather than just noting. Glucagon receptor agonism raises energy expenditure and also acts on the liver, and unlike an appetite effect it is not something a person can feel titrating. A compound that takes a month to reach steady state is a compound whose full effect on liver enzymes and glucose is a month away from the dose change that caused it — which is why the trial monitoring schedules in the app's entry for it are as frequent as they are.
One dose
pkCurve function — a
one-compartment absorption-and-elimination model with the absorption rate fitted so the
peak lands at the published time to peak.Dosed once weekly
Charted at once weekly because that is the schedule used in the published phase II trials. It is what the numbers below are indexed to, not a recommendation about frequency — that is a prescribing decision.
The arithmetic behind those numbers
fraction left after one interval = 2^(−1.12) = 0.460
accumulation ratio = 1 ÷ (1 − 0.460) = 1.85
time to steady state ≈ 5 × half-life = 31.3 days
peak-to-trough = simulated, 1.889 ÷ 0.9824 = 1.92
The accumulation ratio is a closed form; the peak-to-trough figure is not. The generator adds up enough repeated curves for the total to stop changing, then reads the highest and lowest points of the last interval — which is what steady state means in practice. The vertical axis is relative, not a concentration: the shape and the ratios carry across people, the absolute levels do not.
This compound's half-life is an estimate. The app flags it, and every number on this page inherits that. It means the published human pharmacokinetic data is limited or absent and the figure is inferred — so treat the curves as the right shape rather than the right numbers, and treat any claim about exact clearance times with the same caution.
Interaction rules that name Retatrutide
From the app's own interaction data. Not exhaustive, and not a safety clearance — a combination that is not listed is one nobody has documented here, which is not the same as one that is fine. The full combination checker has the rest.
Never Combine GLP-1 Class Agents
Retatrutide and tirzepatide both target GLP-1 receptors. Combining any two GLP-1/GIP/glucagon receptor agonists dramatically increases pancreatitis risk, severe GI events, and provides no additive weight loss benefit beyond one agent at maximum dose.
What to watch: Amylase, lipase if any abdominal pain. Do not combine.
Never Combine GLP-1 Class Agents
Same as above — retatrutide and semaglutide both target GLP-1 receptors. Never combine two agents from this class.
What to watch: Do not combine. If switching agents, appropriate washout period required.
The dosing rows this cadence came from
Established clinical use Reproduced from the app's entry so you can see what the chart above is indexed to. Which row applies to a particular person, if any, is a clinical decision this page does not make.
| Label | Amount | Route and frequency |
|---|---|---|
| Phase II trial doses | 1-12mg/week | Weekly SubQ — titrated over months |
| Estimated clinical | Start 1-2mg/week, titrate | Weekly SubQ |
When to draw bloodwork
The panel the app records for Retatrutide is: HbA1c, fasting glucose, lipids, liver enzymes, body composition monthly, weight weekly.. The pharmacokinetic point is the timing rather than the list: after any change, a level takes about 31.3 days to settle, so a panel drawn sooner measures something still moving. And because the peak-to-trough swing here is 1.92×, when in the interval you draw changes the result materially — a result without a stated draw time relative to the last dose is hard to compare with anything. Whether a result means anything is a question for the clinician who ordered it, read against the reference range your own lab printed. The lab-marker pages cover what the individual analytes measure.
Related: the interactive half-life calculator to try other cadences, and the Retatrutide reconstitution calculator.
The app draws this curve from the doses you actually logged — your dates, your cadence — and projects seven days forward from the last one.
Save this dose to your log