Tirzepatide half-life: how long it stays in your system

Tirzepatide is given once a week because it leaves the body slowly. The half-life, the time for the amount in the body to fall by half, sets how fast levels build during the dose ladder and how fast they fall after the last dose. This page collects what the FDA labels say and shows the arithmetic.

What the labels say

(DailyMed, Aug 28, 2026) (DailyMed, Aug 27, 2026)

The 5–6 day range applies to people with overweight or obesity and people with obstructive sleep apnea and obesity. The Mounjaro figure comes from the type 2 diabetes population and is stated as “approximately 5 days, enabling once-weekly dosing.” Our model uses 5 days for everyone and says so.

The decay formula

For a single dose that has been fully absorbed, the fraction left after t days is:

fraction left = 0.5^(t ÷ t½)

With t½ = 5 days, the elimination rate constant is ke = ln 2 ÷ 5 = 0.1386 per day. After 7 days: 0.5^(7 ÷ 5) = 0.5^1.4 = 0.3789. So about 38% of a weekly dose is still present when the next one is due.

The two columns show how much the label’s range matters. One extra day of half-life leaves about 7 points more drug at day 7, and roughly double the fraction at day 28.

Modeled single dose, including absorption

The table above ignores absorption. In reality, a dose takes time to reach the bloodstream; the Zepbound label gives a median of 24 hours to peak. The table below comes from our model, which adds first-order absorption with a 1-day time to peak. Values are relative amounts for a 1 mg dose.

The model output is a relative amount in mg-equivalents with bioavailability set to 1. It is not a plasma concentration and it is not a measured level. The model card lists every assumption.

Accumulation and steady state

Because about 38% of each dose is still present at the next one, weekly doses stack. For a 5-day half-life, the weekly accumulation ratio is:

R = 1 ÷ (1 − e^(−ke × 7)) = 1 ÷ (1 − 0.3789) = 1.6101

That means, at a constant weekly dose, the modeled amount at steady state is about 1.61 times what a single dose alone would give at the same point in the week. The modeled peak-to-trough swing at steady state, from decay alone, is about 2.6-fold (1 ÷ 0.3789).

The model reaches about 97% of steady state after 5 half-lives, which is 25 days for tirzepatide. The label states that steady state was achieved after 4 weeks of once-weekly dosing. (DailyMed, Aug 28, 2026) The two line up: 25 days is just under 4 weeks.

There is a practical point in this. The label ladder holds each step for at least 4 weeks, which is about the time needed for levels to settle at that step before the next increase.

• Weekly dose (published steps)
• Modeled amount (mg-eq)
• Stable window

The chart shows the label ladder with each step held 4 weeks and the modeled amount rising with each step. See the tirzepatide dosage chart for the label’s dosing rules.

Washout after the last dose

The labels do not state a washout period for tirzepatide. Arithmetic gives an estimate.

After steady-state dosing the starting amount is higher, so the absolute amount at each point is higher too, though the fractions fall at the same rate. If you are stopping before surgery, pregnancy planning or for any other reason, the timing is a prescriber decision. The Zepbound label specifically warns about pulmonary aspiration during general anesthesia or deep sedation and tells patients to inform providers of planned procedures. (DailyMed, Aug 28, 2026)

Why the missed-dose window is 4 days

Both labels say a missed dose can be taken within 4 days (96 hours); after that, skip it and resume on the regular day. They also require at least 3 days (72 hours) between two doses when changing the dose day. (DailyMed, Aug 28, 2026) (DailyMed, Aug 27, 2026) The labels do not explain the reasoning, and we do not add one. The rules are what to follow; ask your prescriber about a specific situation.

Terms on this page, with the label numbers

• Half-life (t½). Time for the amount in the body to fall by half once absorption is done. Label: about 5 days (Zepbound: 5–6 days).
• Time to peak (tmax). Time from a dose to the highest blood level. Label: median 24 hours, with a range of 8 to 72 hours, so some people peak within a day and others closer to three.
• Bioavailability. Share of a subcutaneous dose that reaches the circulation. Label: 80%. Our model sets this to 1 and reports relative mg-equivalents, so its numbers compare schedules rather than estimate absolute amounts.
• Steady state. The point where each week’s dose replaces what was eliminated that week, so the weekly pattern repeats. Label: reached after 4 weeks of weekly dosing.
• Clearance. Volume of plasma cleared of drug per unit time. Mounjaro label: an apparent population mean of 0.061 L/h.

The labels report averages. They do not give the spread of half-life between people, so the model cannot show how much faster or slower any one person clears the drug. The model is a teaching tool for comparing schedules. For anything about your own treatment, ask your prescriber or pharmacist rather than adjusting from a chart.

Run your own schedule

The tirzepatide dose plotter works as a tirzepatide or Zepbound half-life calculator. Enter doses and dates, and it plots the modeled amount over time with the 5-day half-life and 24-hour time to peak. The titration calculator puts the label ladder on a calendar. For how tirzepatide compares with semaglutide, see the semaglutide half-life guide, and for brands and approvals, the tirzepatide hub.