Tirzepatide half-life: when Zepbound and Mounjaro peak

Tirzepatide is the medication in Zepbound and Mounjaro. Its half-life shapes how your week feels on a weekly shot, and it is a little different from semaglutide.

The numbers

According to the prescribing information:

• Half-life: about 5 days
• Time to peak: 8 to 72 hours after the injection
• Steady state: reached after about 4 weeks of weekly doses

What a 5-day half-life means

Every 5 days, the amount of a single dose in your body drops by half. After a week, a bit less than 40% of that dose is left. Each new weekly shot adds to that remainder, so the level builds up over the first weeks on a dose and then settles.

Why the week has more of a swing

With a shorter half-life, more of each dose is cleared before the next shot than with semaglutide (about a 7-day half-life). In a simple model using both published half-lives, once settled:

These are model estimates, not measurements. The takeaway is the shape: on tirzepatide, the difference between the high days and the low days of your week is bigger. Some people notice it as appetite or food noise coming back before shot day.

First weeks on a new dose

Tirzepatide is usually started low and increased step by step, as decided by your prescriber. Each time the dose changes, the level takes a few weeks to settle again. The first week on a new dose is not a fair picture of how that dose will feel once settled.

How long it takes to clear

A common rule of thumb is about 5 half-lives for most of a medication to be cleared: for tirzepatide, about 25 days after the last dose. It varies from person to person.

What this does not tell you

The half-life is not a dosing instruction. Missed doses, changing your shot day and dose changes are covered by the instructions that came with your medication and by your prescriber.

See your own curve

Pick Zepbound or Mounjaro in the GLP-1 level estimator to see your week, and how it changes in your first shots on a dose.

Sources

• Zepbound and Mounjaro prescribing information, section 12.3 (pharmacokinetics): half-life of about 5 days, time to peak 8 to 72 hours, steady state after 4 weeks.
• Model estimates: one-compartment model with first-order absorption, the same one used in the Embera app.