Missed a tirzepatide dose? The 96-hour rule and the 72-hour rule

Both tirzepatide labels carry the same two sentences on timing, and almost every question about a late or moved dose is answered by one of them.

The missed-dose rule

Zepbound label, section 2.3: "If a dose is missed, instruct patients to administer ZEPBOUND as soon as possible within 4 days (96 hours) after the missed dose. If more than 4 days have passed, skip the missed dose and administer the next dose on the regularly scheduled day. In each case, patients can then resume their regular once weekly dosing schedule." The Mounjaro label (section 2.1) says the same with the other name.

Three things follow. The window is measured from the scheduled time, not from when you remembered. The next dose does not move; a late dose does not push your week back. And there is no instruction anywhere to take a larger dose, two doses, or an extra dose to make up.

Worked examples

Your day is Monday, 9 a.m.

• Remembered Wednesday night, 60 hours late: take it now. Next dose the coming Monday as usual.
• Remembered Friday 8 a.m., 95 hours late: inside the window by an hour. The label says take it, then resume Monday. That leaves 73 hours to Monday's dose.
• Remembered Friday noon, 99 hours late: skip. Monday's dose as normal. You will have gone 14 days between injections; the label accepts that rather than have two doses close together.
• Remembered the following Monday: that is the next scheduled dose. Take it. The missed one is simply gone.

The day-change rule

Same section: "The day of weekly administration can be changed, if necessary, as long as the time between the two doses is at least 3 days (72 hours)." That is the whole rule. It does not require a prescriber's sign-off in the label text, it does not say how often you may change, and it applies only to the two doses either side of the change.

Practical reading: to move earlier in the week, you shorten one interval, and the shortened interval must be 72 hours or more. To move later, you lengthen one interval, and lengthening is always allowed as long as you do not drift into missed-dose territory. Monday to Friday is a 96-hour gap and fine; Friday to Monday is 72 hours exactly and also fine; Monday to Wednesday is 48 hours and not.

Why the numbers are what they are

Section 12.3 of the Zepbound label gives an elimination half-life of approximately 5 days and says steady-state concentrations are reached after 4 weeks of weekly dosing. A weekly drug with a 5-day half-life keeps a substantial fraction of the previous dose in circulation at day 7, which is why a dose at day 10 or 11 is a nudge, not a restart, and why a dose at day 3 after the last one would stack. The label does not spell out this reasoning; it is the pharmacology that sits underneath the two rules.

When the rule is not the whole answer

The label rule is about timing only. It assumes the missed dose was an accident and that you are otherwise well. Call your prescriber before injecting if you missed the dose because you were vomiting or could not keep fluids down (the label warns about volume depletion and acute kidney injury), if you missed more than one dose, or if you are mid-escalation and unsure whether the next injection should be the old step or the new one. If you are on compounded tirzepatide, the brand label does not govern your product; your prescriber's written instructions do, and compounded tirzepatide is not FDA approved or interchangeable with Zepbound or Mounjaro.

The helper

The tool above takes the scheduled time and the time you can inject, counts the hours, and states which sentence of the label applies. In its second mode it checks a planned day change against the 72-hour minimum and tells you the earliest time that satisfies it. Both the titration planner and the semaglutide missed-dose rules on the sister site follow the same conventions if you are comparing drugs.