Wegovy® stays in your body for roughly 5 to 7 weeks after the last injection, Mounjaro® for roughly 3 to 5 weeks. Both durations come down to one simple concept: the half-life — the time your body needs to eliminate half of the medication. It explains why a single weekly injection is enough, why the effects don’t vanish overnight when you stop, and why being a few days late is not a catastrophe.
Half-life, explained simply
After an injection, the medication is released slowly and then eliminated gradually. The half-life measures the speed of that elimination:
- Semaglutide (Wegovy®, Ozempic®): about 1 week. Seven days after a dose, roughly half of it is still in your body.
- Tirzepatide (Mounjaro®): about 5 days (120 hours).
- Liraglutide (Saxenda®): about 13 hours — which is exactly why that treatment is injected daily rather than weekly.
A useful rule of thumb in pharmacology: it takes about 5 half-lives for a medication to be almost completely eliminated — and about as long for its level to stabilise when you take it regularly.
Why the level climbs during the first weeks
With one injection per week and a half-life of about a week, each new dose arrives before the previous one has been cleared. The level in your body therefore builds up gradually, then reaches a plateau (“steady state”) after roughly 4 to 5 weeks: what your body eliminates between two injections is then replaced by the next dose.
This is also one of the reasons dose steps last at least 4 weeks: the level is given time to stabilise before judging the effect — and the tolerability — of the current dose.
After stopping: nothing ends abruptly
Conversely, when you stop the treatment, the medication doesn’t disappear instantly:
- Wegovy®: with its roughly one-week half-life, semaglutide remains in the circulation for about 5 to 7 weeks after the last injection.
- Mounjaro®: tirzepatide clears in roughly 3 to 5 weeks.
Two practical consequences: effects (including digestive ones) can linger for a few weeks after stopping. This is why semaglutide’s product information asks for discontinuation ahead of a planned pregnancy, and why the anaesthesia team must be told about the treatment before an operation — decisions to make with your doctor, never on your own.
The link with missed injections
The long half-life is your safety net: a few days’ delay doesn’t erase the previous weeks, because the level only declines gradually. This is what the official catch-up windows are built on — 5 days for Wegovy®, 4 days for Mounjaro®. We cover every scenario in our guide Missed your injection? What to do, day by day.
Seeing your estimated level, week after week
All of this becomes much more concrete on your own curve.
The Doza app draws an estimated level curve from your actual injections, using a classic pharmacokinetic model and the published parameters from the official product information. You can see the climb of the first weeks, the plateau, and the effect of a delay or a missed dose. One important caveat: this is a model-based estimate, not a measurement — only a blood test measures a real concentration. The full methodology is available inside the app.
FAQ — half-life and duration of action
How long does Wegovy stay in your system after stopping?
About 5 to 7 weeks after the last injection, because its half-life is about a week. Effects fade gradually over that period.
How long does Mounjaro stay in your system?
With a half-life of about 5 days, tirzepatide is effectively cleared within 3 to 5 weeks of the last injection.
Why is one injection per week enough?
Because the half-life is long (about 5 days for tirzepatide, one week for semaglutide), last week’s medication is still largely present when the next dose arrives, which keeps the level steady.
What is “steady state”?
The plateau reached after 4 to 5 weeks of regular dosing: elimination between doses is then balanced by each new injection, and the level settles around a stable value.
Do I lose the benefits if I shift an injection by 2 days?
No, in either direction: moving earlier only requires keeping at least 72 hours between two doses, and moving later is covered by the official catch-up windows (5 days for Wegovy, 4 for Mounjaro). The level itself declines only slowly.
Sources: Wegovy® SmPC — EMA (elimination half-life ≈ 1 week; present in the circulation ~7 weeks after the last 2.4 mg dose) · Mounjaro® SmPC — EMA (half-life ≈ 5 days; steady state after 4 weeks) · Saxenda® SmPC — EMA (half-life ≈ 13 hours). General information only: your doctor remains the right person for any treatment decision.