Quick answer: Wegovy (semaglutide) has a half-life of about one week, roughly 165 hours. That means it takes about 7 days for the level in your blood to drop by half. The long half-life is why Wegovy is injected once weekly, why it takes 4 to 5 weeks to reach steady levels, and why it takes about 5 weeks to clear after your last dose. Peak blood levels occur 1 to 3 days after injection, which is usually when side effects are strongest.
Half-life is one of the most useful numbers to understand on Wegovy because it explains the dosing schedule, the timing of side effects, and what happens if you miss a dose or stop. Here is what it means in plain terms. This is general education, not medical advice.
What is the half-life of Wegovy?
Wegovy's half-life is about 165 hours, or roughly 7 days, according to the prescribing information. If you have a given amount of semaglutide in your blood, about half of it is still there a week later. This long half-life is what allows once-weekly injection instead of a daily shot.
Half-life is not the same as "how long the drug works" or "how long until it is completely gone." Those are separate questions covered below.
How long does semaglutide take to leave your system?
It takes roughly 5 half-lives for a drug to be considered cleared, meaning down to a few percent of the starting amount. For Wegovy, that is about 5 weeks (around 35 days) after your last dose. The math runs like this:
- After 1 week, about 50% remains
- After 2 weeks, about 25% remains
- After 3 weeks, about 12.5% remains
- After 5 weeks, about 3% remains, which counts as eliminated
So the common claim that semaglutide is "out of your system in a week" is wrong. One week is one half-life, not full clearance.
Why is Wegovy dosed once a week?
The week-long half-life keeps semaglutide in your blood long enough that a weekly dose maintains steady levels. Shorter-acting GLP-1 medications need daily dosing. Liraglutide (Saxenda, Victoza), for example, has a half-life of about 13 hours, so it must be injected daily to keep working. Semaglutide was engineered to resist rapid breakdown and to bind to blood proteins, which stretches its half-life to about a week and supports weekly dosing.
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Try the BMI Calculator →When does Wegovy reach peak concentration?
Peak blood concentration (Tmax) happens 1 to 3 days after injection. The exact timing varies by person and injection site. This window is usually when appetite suppression is strongest and when nausea and other side effects tend to peak. Many people learn their own pattern and plan meals or events for later in the week when symptoms ease.
How long does Wegovy take to reach steady state?
Steady state is when the amount entering your body each week balances the amount leaving. It takes about 4 to 5 weeks of consistent weekly dosing to get there, which lines up with the 5-half-lives rule.
This explains a pattern that surprises many people: side effects often get worse during weeks 2 to 4 of a new dose, not immediately after the first shot. Each weekly dose adds to what is left from prior weeks, so your average exposure climbs until it plateaus around week 4 to 5. The standard titration schedule, holding each dose for about 4 weeks before increasing, is built around giving your body time to reach steady state and adapt.
What happens if you miss a Wegovy dose?
The prescribing information gives a simple rule based on the half-life:
- If it has been less than 5 days since your scheduled dose, take it as soon as you remember, then resume your normal weekly schedule.
- If it has been more than 5 days, skip the missed dose and take the next one on your regular day.
The 5-day cutoff exists because by then your level has dropped enough that injecting a full dose after a long gap can cause a larger-than-usual spike and worse nausea. If you miss two or more weeks, your provider may have you step back to a lower dose before returning to your maintenance dose. A common error is "doubling up" to catch up, which stacks doses and tends to cause severe nausea, so avoid that.
Half-life vs duration of action: why it works longer than 7 days
Half-life describes how fast the drug clears. Duration of action describes how long the effect lasts. For semaglutide they are not the same. The appetite and blood-sugar effects can persist for 10 to 14 days after a single dose, longer than the 7-day half-life, because GLP-1 receptor activation triggers cell signaling that outlasts the drug molecule itself. Practically, if you stop Wegovy, appetite usually returns gradually over 2 to 3 weeks rather than overnight.
How Wegovy compares to other GLP-1 medications
| Medication | Active ingredient | Half-life | Dosing | Time to steady state |
|---|---|---|---|---|
| Wegovy | Semaglutide | About 165 hours (7 days) | Once weekly | 4 to 5 weeks |
| Ozempic | Semaglutide | About 165 hours (7 days) | Once weekly | 4 to 5 weeks |
| Rybelsus | Oral semaglutide | About 165 hours (7 days) | Once daily | 4 to 5 weeks |
| Mounjaro / Zepbound | Tirzepatide | About 120 hours (5 days) | Once weekly | About 4 weeks |
| Saxenda / Victoza | Liraglutide | About 13 hours | Once daily | A few days |
| Trulicity | Dulaglutide | About 120 hours (5 days) | Once weekly | 2 to 4 weeks |
Semaglutide has the longest half-life of the approved GLP-1 medications. That is an advantage for convenient weekly dosing and stable levels, and a trade-off when you need to change course, since dose reductions and washout take longer than with a short-acting drug like liraglutide.
When half-life matters: switching, surgery, and pregnancy
Switching medications. Because semaglutide takes about 5 weeks to wash out, switching to another GLP-1 means overlapping exposure for several weeks. Providers usually start the new drug on the day the next Wegovy dose would have been due and watch for additive nausea.
Surgery and anesthesia. GLP-1 drugs slow gastric emptying, which raises aspiration risk under anesthesia. Guidance from anesthesiology groups has moved toward an individualized, risk-based approach rather than a single fixed hold for everyone. Your surgical and anesthesia team will tell you whether and how long to hold the medication and may assess stomach contents before a procedure. Follow their specific instructions.
Pregnancy planning. The Wegovy prescribing information advises stopping semaglutide at least 2 months before a planned pregnancy, which accounts for the long washout plus a safety margin.
Frequently asked questions
What is the half-life of Wegovy? About 165 hours, or roughly 7 days, per the prescribing information. The level in your blood drops by half each week.
How long for semaglutide to leave your system? About 5 weeks (around 35 days), which is 5 half-lives. After one week, about half still remains.
What does the Wegovy prescribing information say about half-life? It lists an elimination half-life of approximately 1 week and a time to maximum concentration of 1 to 3 days after dosing.
Is the half-life of Wegovy different from Mounjaro? Yes. Wegovy (semaglutide) is about 7 days. Mounjaro (tirzepatide) is about 5 days. Both support once-weekly dosing.
Why is liraglutide's half-life only 13 hours? Liraglutide is a shorter-acting GLP-1 drug, so it is dosed daily. Its roughly 13-hour half-life is why it cannot be given weekly.
Why do side effects get worse around week 3 or 4? That is when you approach steady state. Each weekly dose adds to residual drug, so average exposure peaks around week 4 before leveling off.
What if I miss a dose by more than 5 days? Skip it and take your next dose on the regular day. Taking a full dose after a long gap can cause a concentration spike and severe nausea.
Why does Wegovy keep working longer than 7 days? Half-life measures drug levels, not effect duration. Receptor signaling keeps appetite and blood-sugar effects going for about 10 to 14 days after a dose.
Sources
- Wegovy (semaglutide) Prescribing Information, pharmacokinetics. Novo Nordisk / FDA. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/125469s037lbl.pdf
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 2021. https://www.nejm.org/doi/full/10.1056/NEJMoa2032183
- Mounjaro (tirzepatide) Prescribing Information, pharmacokinetics. Eli Lilly / FDA. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/215866s000lbl.pdf
- American Society of Anesthesiologists guidance on GLP-1 receptor agonists and perioperative care. https://www.asahq.org
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