Dosage · Pharmacology

GLP-1 Half-Life
Calculator

See how much semaglutide or tirzepatide is still active in your system — and when your concentration drops below therapeutic levels.

Current drug concentration
Active concentration
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of peak level
Time since injection
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Status
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Concentration decay
Results are estimates. Individual results vary. Not medical advice.
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GLP-1 half-lives explained

Semaglutide (Ozempic, Wegovy) has a half-life of approximately 7 days (168 hours), which is why it is dosed once weekly. This long half-life means the medication builds up in your system over the first 4 to 5 weeks until it reaches steady state. At steady state, you always have roughly 2 times the single-dose concentration in your system.

Tirzepatide (Mounjaro, Zepbound) has a shorter half-life of approximately 5 days (120 hours), also dosed once weekly. Because of this shorter half-life, tirzepatide reaches steady state slightly faster and has slightly larger concentration swings between doses.

What happens when you miss a dose: Because GLP-1 medications have long half-lives, missing one dose does not immediately drop your concentration to zero. After 7 days past a missed semaglutide dose, you still have approximately 50% of your peak concentration remaining.

Why half-life matters for dosing

The long half-life of GLP-1 medications creates flexibility — you can inject on any consistent day of the week. It also means that when stopping treatment, appetite does not return immediately; it gradually increases over several weeks as the drug clears your system. This pharmacokinetic property is why abrupt cessation causes a smoother appetite rebound than many patients expect.

Frequently asked questions
Semaglutide has a half-life of approximately 7 days (168 hours). This is why it is dosed once weekly — the long half-life maintains therapeutic levels between doses. At steady state (after 4 to 5 weeks of weekly dosing), semaglutide concentration is approximately twice the concentration from a single dose.
Tirzepatide has a half-life of approximately 5 days (120 hours). Like semaglutide, it is dosed once weekly. The shorter half-life means tirzepatide reaches steady state slightly faster than semaglutide and shows slightly larger concentration fluctuations between doses.
After stopping semaglutide, the drug takes approximately 5 to 7 weeks to clear from your system (5 half-lives = ~35 days). Appetite suppression gradually decreases over this period rather than stopping abruptly. This is why the first 1 to 2 months after stopping are the highest-risk period for rapid weight regain.
If you miss a dose of semaglutide, inject as soon as you remember if no more than 5 days have passed. If more than 5 days have passed, skip the missed dose and resume your regular weekly schedule. Because of the long half-life, missing one dose does not eliminate the medication from your system — you retain approximately 50% concentration 7 days after a missed semaglutide dose.
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