Run your own numbers: Retatrutide Washout Calculator
This page shows one fixed case (5 weeks at 12 mg). Enter your own weekly dose, how many weeks you took it, and the date of your last injection to see the dates your modelled level falls to half, a quarter and under 3% of its peak, and how much is left today.
Open the washout calculator →Key Takeaways
- Compound: Retatrutide (6.0-day half-life, GLP-1/GIP/glucagon triple agonist)
- Protocol length: 12 weeks covering 2 dosing phases
- Steady state: Reached in approximately 4 weeks at each dose level (estimated from the ~6-day half-life)
- Washout: In the model, the level is below 3% of its peak by day 32 after the last dose
- Elimination: The drug clears gradually based on its 6.0-day half-life, with levels halving roughly every 6.0 days
Investigational Drug: Retatrutide is not FDA-approved and is currently in Phase 3 clinical trials. Lilly is reported to plan an FDA filing in early 2027 (HCPLive, AJMC); FDA's usual review times would put a decision in late 2027 or 2028 (our estimate, not Lilly's). This is an illustrative schedule, not a trial protocol.
Retatrutide Washout: How Long Until It Leaves Your System
Quick Answer
Retatrutide has a half-life of 6.0 days. This scenario shows the elimination timeline after stopping Retatrutide. In the model, the level falls below 3% of its peak by day 32 after the last dose. Five half-lives of pure decay would be 30 days; absorption adds about a day, and the count runs to the first whole day under 3%.
Data computed with the same model and parameters as the GLP3Planner calculators: each dose is absorbed over a day or two and then removed at the rate its published half-life sets. The PK methodology lists every parameter and its source.
Understanding the Washout Period
A washout period is the time it takes for a drug to leave your system after you stop taking it. For Retatrutide with its 6.0-day half-life, the drug does not disappear overnight. Instead, levels decrease by roughly half every 6.0 days.
Because the level falls gradually, there is no single day when the drug is gone. Knowing the curve sets realistic expectations for how long Retatrutide stays in your body after a last dose. The curve shows drug level only; it does not tell you when effects or side effects wear off.
The data below models the level after the weekly doses in this scenario. The level keeps rising for a day or so after the last injection while that dose is absorbed, then falls. By day 32 after the last dose the modelled level is below 3% of that peak: about 97% of the peak is gone in the model. The washout calculator uses the same line, so it gives the same day for this schedule. Some drug remains, and this is not a clinical clearance threshold. This page uses the same absorption model as the calculators, described in GLP3Planner's PK methodology. The Retatrutide washout calculator gives the dates for your own dose, number of weeks and last injection.
Dosing Protocol
| Phase | Weeks | Dose | Frequency | Peak (mg) | Trough (mg) |
|---|---|---|---|---|---|
| 12mg (5 weekly doses) | 1-5 | 12mg | 1x/week | 15.45 | 7.66 |
| Stopped (washout) | 6-12 | 0mg | - | 0.06 | 0.03 |
Peak and trough are the highest and lowest modelled amounts in the last week of each phase, from the same model and parameters as the calculators (6.0-day published half-life). See methodology.
A phase with no injection (0mg) has no dosing frequency; its peak is the level at the start of its last week, carried over from earlier doses.
A phase marked "5 weekly doses" starts from zero, so in the model it ends a few percent short of steady state. A later phase at the same dose can therefore show a slightly higher peak.
What the Numbers Mean
The table above shows modeled drug levels at each phase of this protocol. Here is what each column tells you:
Peak (mg)
The highest modelled amount of Retatrutide in your body in the last week of that phase, reached a day or two after an injection once the dose has been absorbed. In a phase with no injection it is the level at the start of the week.
Trough (mg)
The lowest modelled amount in the last week of that phase, reached just before an injection. This is the minimum drug level in the model between doses.
Steady State (~4 weeks)
The point where drug accumulation stabilizes. Before steady state, each dose adds more drug than your body eliminates, so levels keep climbing. Once reached, the amount in equals the amount out, and your peaks and troughs become consistent from week to week.
Washout (~32 days)
The first whole day after the last dose on which the modelled level is below 3% of its peak. With a 6-day half-life, Retatrutide clears gradually, and some drug remains after this line.
These are population-average estimates from the model's parameters, each listed with its source in the methodology. For retatrutide the 80% bioavailability is borrowed from tirzepatide (no figure has been published), and the 1-day time to peak is a median from Phase 1 trials (in the Phase 1b study, blood was sampled mostly 12, 24, 48 and 72 hours after a dose), so treat the figures as approximate. Individual levels vary based on body composition, metabolism, and injection site. For a personalized view, enter your actual doses into the Retatrutide calculator.
Pharmacokinetic Summary
Half-Life
6.0 days
Time for 50% of the drug to be eliminated
Steady State
~4 weeks
Time to reach stable peak/trough levels at each dose
Washout Period
~32 days
Days from the last dose until less than 3% of the peak remains in the model
Model Your Own Schedule
Enter your actual doses and timing to see a personalized PK curve with your real data.
Open Retatrutide CalculatorPractical Tips for This Protocol
What the Model Shows During Washout
The modelled Retatrutide level after the last dose, as a share of its peak a day or so after that dose, from the same model as the calculators (6-day half-life). This is drug level only: the model does not tell you when effects or side effects wear off.
- Day 7 after the last dose: about 50.7% of the peak left
- Day 14 after the last dose: about 22.6% of the peak left
- Day 21 after the last dose: about 10.1% of the peak left
- Day 32: below 3% of the peak, about 97% gone. Some drug remains; this is not a clinical clearance threshold.
Common Side Effects
In Phase 2 trials, the most common side effects of retatrutide were gastrointestinal: nausea (35-60% depending on dose), diarrhea (20-40%), and constipation (20-30%). These effects were most pronounced during the first 1-2 weeks at each new dose level and typically improved with continued use.[1]
Nausea
Most common during the first few days after an injection or dose increase. Smaller meals, bland foods, and staying hydrated can help. Some people find evening injections reduce daytime nausea.
Digestive Changes
Diarrhea or constipation may occur as the drug slows gastric emptying. Adequate fiber, water, and gentle activity help regulate digestion. These effects typically improve within the first 2-3 weeks at each dose.
Reduced Appetite
This is an expected effect, not a side effect. Make sure you are still eating enough protein and nutrients even when appetite is suppressed. Skipping meals entirely can lead to fatigue and muscle loss.
For a comprehensive list including less common effects, see the full Retatrutide side effects guide.
See Your Own Levels
Enter your actual doses and schedule to get a personalized PK curve.
How This Data Was Computed
Levels come from the same pharmacokinetic model as the GLP3Planner calculators, with the same parameters: each dose is absorbed from under the skin over a day or two, only the bioavailable share reaches the body, and the body removes it at the rate the 6.0-day published half-life sets. Doses are added together (superposition) in 1-hour steps to show how weekly doses accumulate. The figures are modelled amounts in milligrams, not blood test results. For retatrutide the 80% bioavailability is borrowed from tirzepatide (no figure has been published), and the 1-day time to peak is a median from Phase 1 trials (in the Phase 1b study, blood was sampled mostly 12, 24, 48 and 72 hours after a dose), so treat the figures as approximate. Read the full methodology, including data sources and model limitations.
Frequently Asked Questions
How long does Retatrutide stay in your system?
Retatrutide has a half-life of about 6 days. After your last dose the level keeps rising for a day or so while that dose is absorbed, then falls with the 6-day half-life. In the model, after weekly doses the level is below 3% of that peak (about 97% gone) by day 32 after the last dose. By half-life arithmetic, five half-lives (30 days) would leave 3.125%; absorption adds about a day in the model. Some drug remains after that. Use the Retatrutide washout calculator to see the modelled dates for your own dose and last injection.
What is steady state for Retatrutide?
Steady state is when drug accumulation stabilizes, meaning the amount entering your system each dose roughly equals the amount eliminated between doses. For Retatrutide, this takes approximately 4 weeks of consistent dosing at the same level (estimated from the ~6-day half-life). Once at steady state, your peak and trough levels become predictable from week to week.
What happens if I miss a dose of Retatrutide?
Retatrutide is investigational and has no FDA-approved label, so there is no label rule for a missed or late dose, and this page does not invent one. Ask whoever supervises your use. With a 6-day half-life, one missed week lowers your level but does not clear the drug. The Retatrutide missed dose calculator models the drop and the recovery for your own dose and the week you missed; that is a model, not a label instruction.
How accurate is the pharmacokinetic data on this page?
The data uses population-average parameters: the half-life, time to peak and bioavailability listed with their sources in the methodology. For retatrutide the 80% bioavailability is borrowed from tirzepatide (no figure has been published), and the 1-day time to peak is a median from Phase 1 trials (in the Phase 1b study, blood was sampled mostly 12, 24, 48 and 72 hours after a dose), so treat the figures as approximate. Individual drug levels vary based on body composition, metabolism, kidney and liver function, and injection site. The model is most useful for understanding accumulation patterns, steady state timing, and comparing dosing approaches rather than predicting exact personal blood levels. See the full methodology for details.
What is the peak-to-trough ratio and why does it matter?
The peak-to-trough ratio measures how much drug levels fluctuate between injections. For once-weekly Retatrutide at steady state, the model's ratio is about 2.0:1: the peak is about 2.0 times the trough. Higher ratios mean bigger swings between injections. Split dosing reduces this ratio in the model by producing smaller, more frequent peaks.
Is retatrutide FDA-approved?
No. As of 2026, retatrutide is an investigational drug in Phase 3 clinical trials (the TRIUMPH program). Lilly is reported to plan an FDA filing in early 2027 (HCPLive, AJMC); FDA's usual review times would put a decision in late 2027 or 2028 (our estimate, not Lilly's). The schedule on this page is illustrative, not a trial protocol; the half-life comes from Phase 1 studies (Lancet, 2022; Cell Metabolism, 2022),[6][8] the time to peak also comes from Phase 1 data, and the bioavailability is the model's assumption. Check ClinicalTrials.gov for the latest trial status.
Can I use this data to plan my own dosing schedule?
This data is for informational and educational purposes. It shows modeled drug levels for a specific protocol, which can help you understand what to expect and have informed conversations with your doctor. For a schedule tailored to your exact doses, use the interactive Retatrutide calculator.
References
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a Phase 2 trial. N Engl J Med. 2023;389(6):514-526. PubMed
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(4):327-340. PubMed
- Novo Nordisk. Ozempic (semaglutide) prescribing information. U.S. Food and Drug Administration. FDA Label
- Eli Lilly and Company. Mounjaro (tirzepatide) prescribing information. U.S. Food and Drug Administration. FDA Label
- Urva S, Coskun T, Loh MT, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b trial. Lancet. 2022;400(10366):1869-1881. PubMed
- StatPearls. Pharmacokinetics, Steady State. National Center for Biotechnology Information. NCBI Bookshelf
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. PubMed
- Novo Nordisk. Wegovy (semaglutide) prescribing information, sections 2.2 and 2.4. DailyMed. DailyMed
- Eli Lilly and Company. Zepbound (tirzepatide) prescribing information, sections 2.1 and 2.3. DailyMed. DailyMed
Medical Disclaimer
This page is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or recommendations. The pharmacokinetic data shown is modeled from population-average clinical trial parameters and does not predict individual drug levels. Always consult your doctor before starting, adjusting, or stopping any medication.
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