Tirzepatide half-life, time to peak and level curve

What does the label say about tirzepatide’s half-life and peak?

Tirzepatide, sold as Mounjaro and Zepbound, has an elimination half-life of approximately 5 days, which the prescribing information Peptrend cites says enables once-weekly dosing. The same section gives the time to maximum plasma concentration as 8 to 72 hours after a subcutaneous dose, a mean absolute bioavailability of 80%, and steady-state concentrations after 4 weeks of weekly administration.

That peak window is the widest of the six presets, a factor of nine from end to end. The preset picks 24 hours, toward the early end, and takes the label’s 5 days as the half-life and its week as the interval. Bioavailability is set to 100%, as it is for every injection preset, so the model counts each logged milligram whole.

What does one dose look like in the model?

One dose climbs for a day and turns over at 87.1% of the logged amount, short of 100% by the elimination that runs during the climb. The absorption rate the app solves from 24 hours is about 3.31 per day, an absorption half-life near 5 hours, so the rise is quick and the curve spends most of the week falling.

The week is 1.4 half-lives long, so the fall goes further than it does for semaglutide, whose half-life matches its interval. By the time the next weekly dose is due, 39.5% of the first is left.

Within the label’s window, the top of the curve moves with the peak time. At 8 hours a single dose would peak near 95% of the logged amount in this model; at 72 hours, near 66%. The half-life alone decides how high a peak at a given hour can be, and reading the absorption curve shows why.

What happens when weekly doses repeat?

The level settles within four to five half-lives, 20 to 25 days, between 143.1% of one logged dose at its highest and 63.7% just before the next injection. The label reports steady state after 4 weeks of weekly dosing, and day 28 is the first weekly dose after that 20-to-25-day window closes.

The settled swing is the widest of the six. The peak is about 2.25 times the trough, because the interval is longer than the half-life and about three-fifths of the level clears each week. A weekly tirzepatide chart therefore reads as a deep sawtooth, and where in the week a reading falls matters more than it does for a daily medication. How long a GLP-1 takes to reach steady state runs the same build-up in a table.

Where does the model part from the label?

• Bioavailability. The label reports a mean of 80% and the model uses 100%, which lifts the whole curve 25% above where the label’s figure would put it. The shape is unchanged.
• Time to peak. 24 hours is one point in a ninefold range, and a single injection is one draw from whatever spread produced that range.
• People differ. The 5-day half-life is a population figure. The model applies it to every dose, and nothing in the app measures how fast any one person clears the drug.

The dulaglutide page makes a clean comparison: the preset shares tirzepatide’s 5-day half-life and weekly interval and differs only in its 48-hour peak. Every constant is editable in Settings › Medication, and the app asks before a preset overwrites them.