GLP-1 half-life: how long semaglutide and tirzepatide stay in your system

What is a GLP-1 half-life?

A medicine's half-life is the time it takes for the amount in your body to fall by half.⁸ If a drug has a half-life of one week, half of it is gone after one week, half of what is left is gone after the next week, and so on. GLP-1 medicines have long half-lives, measured in days, which is why most are taken once a week. The half-life numbers below come from section 12.3, "Pharmacokinetics", of each US label. Pharmacokinetics simply means how the body absorbs, spreads and clears a drug.

An everyday comparison: think of a phone that loses half of its remaining charge every week while switched off. The analogy stops working in two places. Your body first has to absorb the dose, so levels rise for a day or more before they fall. And people clear drugs at different speeds, so the "battery" drains faster for some than for others.

How fast does the level fall after one dose?

Most medicines, GLP-1s included, follow what pharmacologists call first-order elimination: the body removes a fixed share, not a fixed amount, in each half-life.⁸ That gives a simple pattern after a single dose, counted from its peak:

This is plain arithmetic from the definition. It is why a common rule of thumb says about five half-lives clears most of a drug: about 97% is gone. A 2025 review notes that, based on pharmacokinetic studies, women are routinely advised to stop a GLP-1 medicine five half-lives before trying to conceive.⁹ For semaglutide, with a half-life of about a week, five half-lives is about five weeks. That matches the Ozempic label's statement that semaglutide is present in the circulation for about 5 weeks after the last dose.²

Half-life of each GLP-1 medicine

Why do the medicines last so long when the natural hormone lasts minutes? The Victoza label explains that natural GLP-1 is broken down within 1.5 to 2 minutes by enzymes such as DPP-4, which the medicine resists.⁶ Semaglutide and tirzepatide also stick to albumin, a common protein in the blood. The labels say this slows how fast the kidneys clear them and protects them from breakdown.^2,4

The tablets are a special case. Semaglutide tablets reach their peak about an hour after you take them, but the drug itself has the same one-week half-life as the shot, so levels still build up and wash out over weeks.^1,3 For more on the pill, see oral semaglutide for weight loss.

What is steady state, and when is it reached?

Steady state is the point where the amount you take in each week balances the amount your body clears, so the level stops climbing and moves in the same weekly up-and-down pattern. With a weekly dose and a half-life of about a week, some of last week's dose is still there when the next one goes in, so levels build up over the first several doses.

The labels give the timing directly. Steady levels are reached after 4 to 5 weeks of weekly semaglutide (Ozempic label) or daily semaglutide tablets (Rybelsus label), after 4 weeks of weekly tirzepatide (Mounjaro and Zepbound labels) and after 2 to 4 weeks of weekly dulaglutide (Trulicity label).^2,3,4,5,7 These times are for a fixed dose. During the step-up phase, each new dose starts a fresh climb. See the Wegovy and Zepbound dose schedule for how the steps work.

How long does semaglutide stay in your system?

The labels word this slightly differently:

• Ozempic (section 12.3): about 5 weeks after the last dose.²
• Rybelsus and Ozempic tablets (section 12.3): about five weeks after the last tablet.³
• Wegovy (section 12.3): about 5 to 7 weeks after the last 2.4 mg or 7.2 mg shot or 25 mg tablet.¹

This long tail is why the Wegovy, Ozempic and semaglutide tablet labels, in section 8.3, tell prescribers to stop the medicine at least 2 months before a planned pregnancy.^1,2,3 That is the labels' instruction to prescribers, not personal advice. If you are planning a pregnancy or could be pregnant, talk to your care team before changing anything. Our article on GLP-1s, birth control and pregnancy covers what the labels say about the pill and tirzepatide.

The long half-life also matters for other things. The labels note that after an overdose, observation may need to be long because of the half-life.^2,4 And it is part of why missed-dose rules are written in days, not hours; see what the labels say about a missed dose.

What can a GLP-1 level chart or calculator tell you?

Half-life plotters and estimated level charts take your dose dates and apply average label numbers to draw a curve. That can be useful for seeing the general shape: a rise after each dose, a slow fall, a build-up over the first weeks and a long tail after stopping. But it is a model, and it has limits.

• It uses averages. The Wegovy label shows how wide real levels are. In its model of adults with overweight or obesity without type 2 diabetes, 90% of people on the 2.4 mg weekly shot had average semaglutide levels between 51 and 110 nmol/L. On the 25 mg daily tablet, the range was wider: 27 to 186 nmol/L.¹ The Zepbound label lists person-to-person variation of about 20% in how fast tirzepatide is cleared.⁴
• It is not a blood test. No home chart measures your actual level, and the labels do not call for measuring blood levels of these medicines.
• Feelings do not map exactly onto levels. Appetite, nausea and energy depend on many things besides the level on a given day, such as food, sleep and how long you have been on a dose. A chart can help you notice patterns, but it cannot explain every good or bad day.

Key terms in this article

• Half-life: the time it takes for the amount of a drug in the body to fall by half.
• Pharmacokinetics: how the body absorbs, spreads and clears a drug (label section 12.3).
• Peak: the highest level after a dose, before clearing outpaces absorption.
• Steady state: the point where each dose balances what the body clears, so levels stop building up.
• Washout: the time it takes for a drug to leave the body after the last dose.
• Albumin: a common blood protein; semaglutide and tirzepatide bind to it, which makes them last longer.
• DPP-4: an enzyme that breaks down the body's own GLP-1 within minutes.