"Tirzepatide half-life" is searched for three reasons: how long one injection lasts, how long the drug stays after the last one, and why the schedule is weekly. The labels answer the first in a phrase, the phase 1 study in numbers, and the third in a clause. This page sets out those figures with their dates, works them into the quantities people actually ask about — how much remains a week later, how the level builds, what the missed-dose rule means in the blood — and says where the arithmetic stops.
The dose steps, units and vial arithmetic are on the tirzepatide dosage page; the compound itself is covered in Medibact's Tirzepatide guide.
Two labels, two phrasings
Eli Lilly markets tirzepatide under two names with two labels, and their pharmacokinetics sections do not read identically.
| Label (openFDA version) | Half-life wording | Population named |
|---|---|---|
| MOUNJARO, effective 2026-08-27 | "approximately 5 days, enabling once-weekly dosing" | Type 2 diabetes; pediatric patients 10 years and older analysed separately |
| ZEPBOUND, effective 2026-08-28 | "approximately 5-6 days" | Overweight or obesity, and obstructive sleep apnea with obesity |
The other figures are close: apparent clearance about 0.06 L/h in both, volume of distribution about 10 L, 80% absolute bioavailability after injection under the skin, 99% bound to plasma albumin, steady state after 4 weeks. ZEPBOUND gives a median time to peak of 24 hours (range 8 to 72); MOUNJARO gives the range only. The labels also state that age, sex, race, body weight and kidney or liver impairment have no clinically relevant effect on tirzepatide's pharmacokinetics.
The measurement behind "about 5 days"
The first human data are in Lilly's discovery-to-clinic paper (Coskun et al., Molecular Metabolism 2018, PMID 30473097; full text via PubMed Central). In the single-ascending-dose part, healthy participants received one injection of 0.25 to 8 mg:
| Single dose | Participants | Median time to peak | Half-life, geometric mean (min–max) |
|---|---|---|---|
| 0.25 mg | 6 | 48 h | 116 h (94.6–132) |
| 0.5 mg | 12 | 48 h | 124 h (94.4–163) |
| 1 mg | 5 | 24 h | 106 h (92.9–117) |
| 2.5 mg | 6 | 24 h | 120 h (102–137) |
| 5 mg | 5 | 24 h | 123 h (99.9–147) |
| 8 mg | 7 | 48 h | 111 h (99.6–121) |
The paper summarises the mean as approximately 5 days (116.7 hours) and states the pharmacokinetics support once-weekly administration. Two things follow from the table. The half-life does not change with dose across a 32-fold range, which is what "exposure increases in a dose-proportional manner" on the labels means. And individual values ran from about 3.9 to 6.8 days, so "5 days" is a centre, not a number that holds for every person. The authors are Lilly employees, and the study was the manufacturer's.
What remains, week by week
With a half-life of t days, the fraction of a dose left after d days is ½ raised to d/t. The table works that for the labels' two ends:
| Days after one dose | At 5 days | At 6 days |
|---|---|---|
| 3 (72 h) | 66% | 71% |
| 4 (96 h) | 57% | 63% |
| 7 | 37.9% | 44.5% |
| 14 | 14.4% | 19.8% |
| 21 | 5.4% | 8.8% |
| 28 | 2.1% | 3.9% |
| 35 | 0.8% | 1.8% |
This is elimination arithmetic from the stated half-life; it ignores the day or so of absorption at the start, so the first days are approximate. It answers "how long does tirzepatide stay in the system" in the only form the record supports: there is no single day on which it is gone, and neither label names one. The pharmacology convention of five half-lives for "effectively cleared" gives about 25 days at 5 days and 30 at 6.
How it builds up with weekly doses
Because more than a third of each dose is still present when the next is given, weekly injections stack. The steady-state level is higher than a single dose's by the accumulation factor, 1 ÷ (1 − fraction remaining at 7 days):
| Weekly doses at one strength | Share of steady state, 5-day half-life | Share at 6 days |
|---|---|---|
| 1 | 62% | 56% |
| 2 | 86% | 80% |
| 3 | 95% | 91% |
| 4 | 98% | 96% |
The accumulation factor is about 1.6 at 5 days and 1.8 at 6 days. The label's "steady state after 4 weeks" is the same fact stated from the other end. It is also why the labels hold each dose for at least 4 weeks before a 2.5 mg step up: each new strength starts its own approach to a new plateau.
What the half-life explains in the label's rules
Two instructions in section 2 of both labels are half-life rules in disguise:
- Missed dose: 4 days (96 hours). A dose taken within 4 days of when it was due is given; after 4 days it is skipped. At that point, by the arithmetic above, 57 to 63% of the previous dose is still circulating.
- Changing the dosing day: at least 3 days (72 hours) apart. At 72 hours, 66 to 71% of the previous dose remains, so two doses closer than that would roughly add together.
The labels state the rules; they do not print the reasoning. The percentages are this page's arithmetic from the labels' own half-life.
A third rule sits on the gastric-emptying effect rather than on the half-life. Tirzepatide slows stomach emptying most after the first dose — the ZEPBOUND label reports a 55% fall in acetaminophen peak concentration after a first 5 mg dose and no meaningful effect by week 4 — and both labels' contraception advice follows that window rather than the half-life: a non-oral method, or an added barrier method, for 4 weeks after starting and for 4 weeks after each dose increase, because the effect on oral contraceptives "is largest after the first dose and diminishes over time".
Half-life against the other weekly GLP-1 medicines
| Molecule | Label half-life | Share left at 7 days | Weekly accumulation |
|---|---|---|---|
| Tirzepatide | about 5 days (5–6 in obesity) | 38–45% | about 1.6–1.8 |
| Semaglutide (WEGOVY) | about 1 week | about 50% | about 2 |
| Retatrutide (no label; phase 1b) | about 6 days | about 45% | about 1.8 |
The semaglutide row is from the WEGOVY label, the retatrutide row from a trial publication, because no retatrutide label exists; that page is retatrutide's half-life, as measured. The full twelve-product table is the GLP-1 dosage chart.
Units, for the doses the half-life is about
Units on a U-100 syringe = mg ÷ mg/mL × 100. At 10 mg/mL, 2.5 mg is 25 units, 5 mg is 50 units and 7.5 mg is 75 units; at 20 mg/mL they are 12.5, 25 and 37.5. The half-life does not change with the concentration in a vial, only the volume that carries a given dose does. The tirzepatide reconstitution page works every vial size, and the calculator's tirzepatide setting works any other.
What is not established
The labels state a half-life for the approved products; none states how long tirzepatide remains detectable. For surgery, both labels' warning on pulmonary aspiration under anaesthesia asks only that planned procedures be disclosed to the treating team; neither label sets a stopping interval for surgery or for switching medicines. The phase 1 figures are single doses in 41 healthy adults. The week-by-week and accumulation figures are arithmetic from a stated half-life, not measurements. Nothing here is a dose or a schedule; those belong with a prescriber.
Sources and dates
Opened 2026-09-25: the MOUNJARO label via openFDA (set id d2d7da5d-ad07-4228-955f-cf7e355c8cc0, effective 2026-08-27) and the ZEPBOUND label via openFDA (set id 487cd7e7-434c-4925-99fa-aa80b1cc776b, effective 2026-08-28), sections 2 and 12.3, filtered to the manufacturer's own copy; Coskun et al., Molecular Metabolism 2018 (PMID 30473097, PMC6308032), Table 2 and section 3.2.2; the WEGOVY half-life as cited on this site's semaglutide pages. Percentages, accumulation factors and steady-state shares are arithmetic by this site. Corrections go to the contact page.