How long a GLP-1 stays in your system

A drug's half-life is the time for its level in the blood to fall by half. After five half-lives about 97 percent is gone, which is the usual definition of "cleared." The weekly GLP-1s were engineered for long half-lives, which is what makes a once-a-week shot possible and also what makes them slow to leave.

What the numbers mean in practice

Missed doses. With a week-long half-life, being three days late on semaglutide barely changes the level in your blood, which is why the label lets you take it. Past about five days you are close enough to the next scheduled dose that the two would stack. Tirzepatide's shorter half-life gives a shorter window, four days. The missed dose page has each rule.

Steady state. Because each weekly dose lands before the last one has gone, the level in your blood climbs for the first four to five weeks on any dose and then flattens. That is why side effects are worst in weeks one and two of a step and why the labels hold each step for four weeks before the next.

Surgery and sedation. Anaesthesia guidance has moved on this. Because the drugs slow stomach emptying, there is a risk of food still being in the stomach under sedation. Current US guidance from the anaesthesia societies generally allows continuing the drug for most people but asks about symptoms and may adjust fasting. Tell the anaesthetist, and tell them the date of the last dose. The log has it.

Pregnancy. The Wegovy and Zepbound labels advise stopping at least two months before a planned pregnancy, because of the long half-life. That is a label instruction, not a suggestion.

Stopping. Appetite returns on the clearance curve, so expect the first noticeable change around week two after the last shot and the full return by the time the drug is gone. The stopping page covers the year after.

Why the pills clear faster

Oral semaglutide is the same molecule as the injection, so it has the same half-life; the daily tablet simply replaces a weekly depot with a daily top-up. Foundayo is different. Orforglipron is a small molecule, not a peptide, with a half-life in the range of a day or two, which is why it is taken daily and why it leaves within about a week. Liraglutide, the older daily injectable, is in between.

Estimating the level in your body

Several apps draw an estimated drug level curve from your dose dates and the half-life. It is a model, not a measurement, and it does not change any rule above. Where it earns its place is in explaining why Thursday feels different from Monday, and why the first week on a new step is rough. Peptide AI's half-life entry explains the maths, and the app's dose log is the input.