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An estimate from the doses and published half-lives, not a blood level. Never change a dose or a schedule because of it: ask your prescriber.
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Zepbound half-life calculator: how long it lasts
Zepbound's label gives tirzepatide a half-life of about 5 to 6 days, close to the 5 days on the Mounjaro label for the same medicine. This page opens the half-life calculator on Zepbound® at 5 mg, offering the label's doses from 2.5 mg to 15 mg. Give it the number of weekly shots so far and the date and time of the latest, and you get an estimate of the tirzepatide in your body today and of when it fades. The estimate is built from label figures rather than a blood result, and choosing a dose stays with the prescriber.
What does the Zepbound label say about its half-life?
The Zepbound prescribing information words it in two places. Its clinical pharmacology section (§ 12.3) says: "The elimination half-life is approximately 5-6 days in patients with overweight or obesity, and in patients with OSA and obesity." Its overdosage section (§ 10) says approximately 5 days, which is also the figure on the Mounjaro label for the same medicine.
The calculator uses 5 days, or 120 hours, for every tirzepatide page. With 6 days, each halving in the table below would take a day longer. The main half-life calculator page explains the rest of the model.
The doses on this page are the ones in § 2.1 and § 2.2 of the Zepbound label:
| Zepbound dose | On the label |
|---|---|
| 2.5 mg | For starting treatment only, for 4 weeks; not approved as a maintenance dose |
| 5 mg | From week 5; a maintenance dose for weight reduction |
| 7.5 mg, 12.5 mg | Steps of 2.5 mg, each after at least 4 weeks on the dose before |
| 10 mg | A maintenance dose for weight reduction and for obstructive sleep apnea |
| 15 mg | A maintenance dose for both, and the maximum |
The prescriber chooses the maintenance dose and the pace of any step.
A worked example: the weeks after a final 15 mg shot
The doses in this example are illustrative. Picture 12 weekly shots of 15 mg and then a stop. Week by week after that last shot, the calculator estimates:
| After the last shot | Estimated amount | Share of the peak |
|---|---|---|
| 1 day (about the peak) | 17.05 mg | 100% |
| 1 week | 7.66 mg | 45% |
| 2 weeks | 2.90 mg | 17% |
| 3 weeks | 1.10 mg | 6% |
| 4 weeks | 0.42 mg | 2% |
| 5 weeks | 0.16 mg | 1% |
Less than half is left a week after the shot. That is why the level dips between weekly shots more than a semaglutide level does: a 5-day half-life is shorter than the 7 days between doses.
How long does Zepbound take to clear?
From that final shot, the estimate falls below 10% of its peak at about 18 days, below 3% at about 27 days and below 1% at about 34 days. The dose does not move those days: 5 mg and 15 mg fade on the same schedule, from different heights.
What can this estimate not tell you?
- What a test of your blood would show. Absorption and clearance vary from person to person, and the 5 to 6 day wording on the label is itself a range.
- How your sleep apnea or weight responds. The Zepbound label ties no level of tirzepatide to either.
- The right Zepbound dose. Its label leaves the choice between 5, 10 and 15 mg to the prescriber, and so does this page.
Frequently asked questions
What is the half-life of Zepbound?
Approximately 5 to 6 days in people with overweight or obesity, according to § 12.3 of its label, and approximately 5 days in its overdosage section. The calculator uses 5 days.
How long does Zepbound stay in your system after the last shot?
In the calculator, under 3% of the last peak is left about 27 days after the final shot, and under 1% after about 34 days.
Does the Zepbound vial last as long as the pen?
The label gives the same doses for every presentation, pens and vials alike, and the same medicine is inside. The calculator treats them the same way.
Where do I see the Zepbound dose steps by week?
The Zepbound dose chart shows the label's steps and both sets of maintenance doses. The Mounjaro half-life page covers the same medicine under its diabetes label.
Sources
- Zepbound (tirzepatide) prescribing information, DailyMed: half-life of approximately 5-6 days (§ 12.3) and approximately 5 days (§ 10); doses, maintenance doses and the maximum (§ 2.1, § 2.2).
- Mounjaro (tirzepatide) prescribing information, DailyMed: half-life of approximately 5 days (§ 12.3).
Published by Petros IT Solutions SRL. Read our editorial policy, and send corrections to office@doseandlose.com.