Tirzepatide Half-Life: How Long Mounjaro and Zepbound Last
Tirzepatide's elimination half-life is approximately 5 days, according to the FDA label for Mounjaro. With a weekly schedule, about 38 percent of a dose is left when the next one is due, and steady state is reached after 4 weeks of once-weekly use. After about 25 days, which is five half-lives, roughly 3 percent remains.[1]
Tirzepatide 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 tirzepatide?
Tirzepatide's elimination half-life is approximately 5 days, according to the prescribing information for Mounjaro, the once-weekly injection from Eli Lilly and Company.[1] The same label gives an apparent population mean clearance of 0.061 liters per hour.[1] Elimination half-life is the time for the amount of drug in the body to fall by half after absorption is done. Five days is shorter than the seven-day gap between weekly doses, so by the time the next injection is due, more than half of the earlier dose has gone. Simple math gives the share left at day 7: 0.5 raised to the power of 7 divided by 5, which is 37.9 percent. That is a different shape from semaglutide, whose half-life is about equal to its interval. The calculator above is preset to 5 days, which is 120 hours. You can edit it, but the value does not change with the size of a dose.
How long does tirzepatide stay in your system?
Using the label's half-life of about 5 days, five half-lives is 25 days, and about 3 percent of a dose remains by then.[1] The percentages come from halving: 50, 25, 12.5, 6.25, and 3.1 percent. The table lists them alongside PepTrac's modeled level for one 1 mg dose, which is a little higher than the plain halving at day 7 because the dose peaks about a day after injection. The model decline therefore starts one day late. At day 14 the modeled level is about 0.17 of the peak, and by day 28 it is about 0.02, with a range of 0.01 to 0.05. These are estimates. The label does not say that the drug is undetectable after a fixed number of days, and your own clearance can differ from the population average. Half-life also says nothing about how long effects last.
| Days after dose | Simple share left | Model level (range) |
|---|---|---|
| 5 | 50% | 0.60 (0.50 to 0.67) |
| 7 | 37.9% | 0.45 (0.36 to 0.53) |
| 10 | 25% | 0.30 (0.21 to 0.38) |
| 14 | 14.4% | 0.17 (0.11 to 0.24) |
| 21 | 5.4% | 0.07 (0.03 to 0.11) |
| 25 | 3.1% | 0.04 (0.02 to 0.07) |
| 28 | 2.1% | 0.02 (0.01 to 0.05) |
How does tirzepatide's half-life compare with semaglutide's?
Tirzepatide's label half-life is about 5 days and semaglutide's is about 1 week, so tirzepatide clears faster.[1][3] The gap changes the weekly curve in a way you can see in numbers. After a week, half of a semaglutide dose is left, against 37.9 percent for tirzepatide. If you repeat the doses each week, semaglutide builds up to twice a single dose's level, and tirzepatide to about 1.6 times. In PepTrac's model, the steady-state level just before the next dose is about 1.31 for semaglutide and 0.73 for tirzepatide, and the peak after a dose is about 2.10 against 1.64. Tirzepatide's peak is more than twice its low point, while semaglutide's is about 1.6 times its low. A shorter half-life does not mean a drug works less well. It only describes how fast the amount in the body falls, and it says nothing about effect.
| Measure | Semaglutide | Tirzepatide |
|---|---|---|
| Label half-life | about 1 week[3] | about 5 days[1] |
| Label time to peak | 1 to 3 days[3] | 8 to 72 hours[1] |
| Label steady state | 4 to 5 weeks[3] | 4 weeks[1] |
| Share left after 7 days (simple) | 50% | 37.9% |
| Weekly build-up ratio (simple) | 2.00 | 1.61 |
| Five half-lives | 35 days | 25 days |
| Model level at day 7, one dose | 0.65 | 0.45 |
| Model level before next dose at plateau | 1.31 | 0.73 |
| Model peak at plateau | 2.10 | 1.64 |
| Label missed-dose window | within 5 days[3] | within 4 days (96 hours)[1] |
How long until tirzepatide reaches steady state?
The Mounjaro label states that steady-state plasma concentrations were achieved following 4 weeks of once-weekly administration.[1] Steady state is the point where the amount cleared each week equals the amount added, so the level before each dose stops rising. The general pharmacokinetic rule is that this takes about five half-lives.[4] Here the shorter half-life matters, because five days leaves less carried over from week to week. PepTrac's model reaches the plateau quickly with weekly 1 mg doses: the level before the fourth dose is about 0.72, which is 99 percent of the final 0.73. The model's range at the plateau is 0.51 to 0.96, so the single figure hides real uncertainty. The values are relative to one dose's own peak and are not blood concentrations. Dose size changes the height of the plateau, not the time needed to reach it.
| Doses taken | Level before next dose | Share of plateau |
|---|---|---|
| 1 | 0.45 | 62% |
| 2 | 0.63 | 86% |
| 3 | 0.69 | 95% |
| 4 | 0.72 | 99% |
| 8 | 0.73 (range 0.51 to 0.96) | 100% |
What does a missed week do to tirzepatide levels?
Because tirzepatide clears faster than semaglutide, a skipped week removes more of the level. In PepTrac's model, after eight weekly doses the level just before the next dose is about 0.73. If that dose is skipped, the level a week later is about 0.28, with a range of 0.15 to 0.43, which is a drop of roughly 62 percent. The same skip with semaglutide halves the level. This is a model about concentration, not guidance on what to do. The Mounjaro label says that if a dose is missed, it should be administered as soon as possible within 4 days (96 hours) after the missed dose.[1] Semaglutide's Ozempic label uses a 5 day window.[3] Those windows are set by the labels, and your prescriber may give you different directions, so ask before you change a schedule.
When does tirzepatide peak after an injection?
The Mounjaro label says that, after subcutaneous injection, the time to maximum plasma concentration of tirzepatide ranges from 8 to 72 hours.[1] The Zepbound label, which covers the same molecule, gives a median of 24 hours within that same range.[2] PepTrac's calculator uses 24 hours to shape the curve. The range is wide, and that is one reason the chart shows a shaded band instead of a single line. After a dose, the level rises while the drug is absorbed, reaches a top, and then falls at the pace of the half-life. A peak at 8 hours and a peak at 72 hours would draw the first days of the curve differently, although both would decline at the same rate afterwards. Peak time varies between people, so no calculator can name the hour your own level tops out.
Do Mounjaro and Zepbound have the same half-life?
Both are tirzepatide from Eli Lilly and Company, and their labels give nearly the same figure. Mounjaro states an elimination half-life of approximately 5 days.[1] Zepbound states approximately 5 to 6 days in patients with overweight or obesity, and in patients with obstructive sleep apnea and obesity.[2] Both labels report that steady state is reached following 4 weeks of once-weekly use.[1][2] The calculator above uses 5 days, the lower figure. Entering 6 days in the half-life box would stretch the curve slightly and push the time to five half-lives from 25 to 30 days. Compounded tirzepatide is a different case. The FDA states that compounded drugs are not FDA approved, so it does not review them for safety, effectiveness, or quality before they are marketed.[5] Do not assume a label half-life applies to a vial from a compounder.
Frequently asked questions
Is tirzepatide out of your system in a week?
No. With a half-life of about 5 days, roughly 38 percent of a dose is still present after 7 days by simple halving. It takes about 25 days, five half-lives, to fall to around 3 percent.
Does the dose, such as 2.5 mg or 15 mg, change the half-life?
No. Half-life reflects how the body clears the drug, so it stays about the same at any dose. A higher dose raises the level, but the level still halves in about 5 days. Doses are set by your prescriber.
Why are the peak times a range?
The label reports 8 to 72 hours because people absorb the drug at different speeds. Because the peak time is uncertain, PepTrac shades a range around its curve instead of drawing one precise line.
Why does PepTrac show 0.45 at day 7 when the half-life math says 38 percent?
The simple 38 percent counts decline from the moment of injection. The model peaks about a day later and scales to that peak, so only six days of decline remain at day 7. Six days of halving gives about 43 percent, close to 0.45.
Does a shorter half-life mean it works less well?
No. Half-life describes how fast the amount in the body falls. It does not measure strength, results, or how long effects last. Do not compare drugs by half-life alone.
Does this tell me when to inject?
No. The calculator is educational and never suggests a dose or timing. Your prescriber and the product label set the schedule, including what to do after a missed dose.
Sources
- DailyMed, National Library of Medicine (Eli Lilly). Mounjaro (tirzepatide) injection prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Eli Lilly). Zepbound (tirzepatide) prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Novo Nordisk). Ozempic (semaglutide) injection prescribing information. 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.
- U.S. Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. 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.
