How long GLP-1 medicines stay in your system
Half-lives, steady state, and the arithmetic behind a missed dose — including why stopping does not mean the effect ends that week.
The short version
- Semaglutide's half-life is about 160 hours — roughly seven days.
- Tirzepatide and dulaglutide are close to five days. Liraglutide is about 13 hours.
- Levels stabilise after about five half-lives: four to five weeks for semaglutide, around 25 days for tirzepatide.
- After a final dose, a weekly medicine takes over a month to clear.
Half-life is the time it takes for half of a drug to leave your body. It is one number, and it explains more about GLP-1 treatment than almost anything else: why the injection is weekly, why the first month feels underwhelming, why missing a dose is survivable, and why appetite does not come back the day you stop.
| Molecule | Half-life | Steady state | Dosing |
|---|---|---|---|
| Semaglutide | ~160 h (~7 days) | 4–5 weeks | Weekly |
| Tirzepatide | ~5 days | ~25 days | Weekly |
| Dulaglutide | ~5 days | ~3–4 weeks | Weekly |
| Liraglutide | ~13 h | ~3 days | Daily |
Why the first month underdelivers
When you inject weekly and the drug takes a week to halve, each dose lands on top of what is left of the last one. Levels accumulate, and keep accumulating, until elimination balances intake. That takes about five half-lives.
So a person on semaglutide is not at their starting dose's full effect until roughly week five — by which point the schedule has already moved them up a step. The sensation of "this is barely doing anything" during month one is accurate and temporary.
What a missed dose actually costs
Consider semaglutide with a seven-day half-life. On the day your next injection is due, roughly half of the previous dose is still present. Two days late, around 80% of the expected level remains. This is why guidance for weekly products generally allows taking a missed dose within a few days rather than treating it as a lost week.
The corollary matters more: because levels fall slowly, taking a late dose and then returning to your normal day does not create a dangerous overlap in the way it would with a short-acting medicine. The specific rules per product are here — they differ, and the difference is worth knowing before you need it.
Daily products behave differently. Liraglutide clears in a few days. A missed dose is a real gap, and if several days are missed, a prescriber may restart the escalation from a lower dose rather than resuming where you left off — the gut loses its adaptation quickly.
Stopping
After a final weekly dose, the drug is largely gone in about five weeks. The appetite effect fades along that curve rather than switching off, which is why people often describe the return of hunger as something that crept up on them over a month rather than an event.
This has a practical consequence worth planning for. The window in which appetite is returning but not yet fully back is the window in which habits either hold or do not. It is a much better time to have a plan than to improvise.
What half-life actually measures
Half-life is not how long a drug works, and it is not how long it stays detectable. It is the time taken for the concentration in your blood to fall by half. Everything else — the dosing interval, the escalation schedule, the missed-dose window — is derived from it.
The reason it dominates this class is that these molecules were engineered specifically to have a long one. Natural GLP-1 is destroyed within minutes by an enzyme called DPP-4. Making a usable medicine meant building a copy that resists that enzyme and binds to albumin, a carrier protein in the blood, so the kidneys clear it slowly. The result is a half-life measured in days rather than minutes — and a weekly injection instead of a continuous infusion.
Accumulation: why levels keep climbing
When the dosing interval is shorter than the time it takes to clear a dose, doses overlap. Each injection lands on what remains of the last one, and the level climbs — not indefinitely, but until elimination balances intake.
The arithmetic is straightforward. After one half-life, half of a dose remains. After two, a quarter. After five, about 3% — close enough to nothing that the level is considered stable. This is why five half-lives is the standard rule for reaching steady state, and why it applies equally on the way down.
| Half-lives elapsed | Remaining | Semaglutide | Tirzepatide |
|---|---|---|---|
| 1 | 50% | ~7 days | ~5 days |
| 2 | 25% | ~2 weeks | ~10 days |
| 3 | 12.5% | ~3 weeks | ~15 days |
| 4 | 6% | ~4 weeks | ~20 days |
| 5 | 3% | ~5 weeks | ~25 days |
Why the first month feels like nothing
Put accumulation together with a starting dose that is deliberately sub-therapeutic, and the first month resolves into something predictable rather than disappointing.
You are taking a dose chosen for tolerance rather than effect, and you are not yet receiving all of even that dose, because the level is still climbing. By the time semaglutide reaches its plateau at the starting dose, the schedule has already moved you up a rung — so in a sense you never experience a stable starting dose at all. You experience a rising level throughout.
This is why "it isn't working" at week three is not evidence of anything. The question worth asking is not whether it is working yet but whether the side effects at each new rung settle by the third week.
Why escalation waits four weeks
The four-week step is five half-lives for semaglutide, near enough. It is the interval at which the previous increase has fully expressed itself, so the next one starts from a known position rather than a moving one.
Escalating faster means stacking. The level from the previous dose has not finished rising when the next arrives, and the two climbs superimpose. The resulting nausea is often read as intolerance to the medicine when it is intolerance to the schedule — a distinction that matters, because one leads to stopping and the other to waiting.
Liraglutide's weekly steps follow the same logic at a different scale: with a 13-hour half-life, steady state arrives in about three days, so a week between steps is already generous.
Stopping, and the month afterwards
The same arithmetic runs in reverse. After a final weekly dose the drug is largely gone in about five weeks, and the appetite effect fades along that curve rather than switching off.
People consistently describe the return of hunger as something that crept up on them rather than an event, and that is exactly what the curve predicts. Week one after stopping feels much like week one before. Week four does not.
The practical consequence is worth planning for: the window in which appetite is returning but has not fully returned is the window in which habits either hold or do not. It is a far better time to have a plan than to build one while it is happening.
What this does not tell you
Half-life describes the drug in your blood. It does not describe the effect, which lags behind concentration and does not track it linearly, and it says nothing about how much weight you will lose or how you will feel. Two people at identical blood levels can respond very differently.
What it does explain is the shape of the treatment: why it starts slowly, why it is escalated on a fixed timetable, why a missed dose is survivable, and why neither starting nor stopping is an event. That shape is the same for everyone, even when the outcome is not.
Sources
- Hall S. et al. Pharmacokinetics and clinical implications of semaglutide. PubMed.
- Hall S. et al. Semaglutide. StatPearls, National Library of Medicine.
- US Prescribing Information for the products named above.
Related
- How GLP-1 medicines actually work — Not appetite suppressants, not fat burners. They are copies of a gut hormone your body already makes — which explains almost everything.
- What to expect, month by month — A realistic timeline of the first year — what usually happens when, and which of it means something.
Which medicine you are on
Everything above applies across the class, because it comes from a shared mechanism. The numbers that differ — dose ladders, missed-dose windows, in-use storage periods, half-lives — differ by product, sometimes substantially. Each medicine has its own reference here:
Ozempic · Wegovy · Mounjaro · Zepbound · Rybelsus · Saxenda · Victoza · Trulicity · all medicines
How this page is sourced. Figures come from manufacturers' approved labelling and from published clinical and pharmacokinetic literature. Regional labels differ, sometimes materially — where a number matters, the leaflet in your own box outranks anything written here. This site is not written or medically reviewed by clinicians, and we say so rather than implying otherwise; our editorial standards set out what that means and how corrections work.