How long does semaglutide stay in your system? Understanding its half life

The pharmacokinetic evidence behind the seven-day figure

The ~seven-day half life of semaglutide is not a rough estimate; it is derived from formal pharmacokinetic studies submitted as part of the regulatory package reviewed by the MHRA and reflected in the Wegovy Summary of Product Characteristics, available on the Electronic Medicines Compendium. In those studies, semaglutide reached peak plasma concentration roughly one to three days after each injection, then declined slowly, roughly halving in concentration each week.

Because the half life equals the dosing interval almost exactly, each new weekly dose arrives just as the previous dose is at roughly half its original concentration. That overlap is by design. It produces a relatively stable drug level in the blood rather than the peaks and troughs associated with daily medicines. By week four or five of continuous weekly dosing, concentrations plateau at what pharmacologists call steady state.

The STEP 1 trial, published in the New England Journal of Medicine, studied once-weekly semaglutide 2.4mg over 68 weeks and observed around 15% average body-weight reduction. That efficacy profile rests on participants maintaining those stable drug levels week on week, the dosing schedule is engineered around the half life, not the other way round.

What happens if you miss a dose or stop treatment

A practical consequence of a seven-day half life is that a single missed injection does not produce an immediate clinical cliff. The NHS semaglutide medicines page advises taking a missed dose as soon as you remember, provided the next scheduled dose is still at least five days away; if it is closer than that, skip the missed dose and resume on your usual day. Your prescriber and the Patient Information Leaflet are the right places to confirm this for your specific situation.

Stopping Wegovy is a different matter. After your last injection, semaglutide clears slowly: roughly half gone after one week, three-quarters gone after two, but detectable concentrations persist for around five weeks. Appetite and body weight typically begin to drift back during that washout window, which is why clinical trials and NHS guidance both flag that the benefits of Wegovy largely depend on continued use. The question of how long you need to stay on Wegovy is one our prescribers explore with every patient at review.

For those considering switching from the injectable to the newer oral format, the half life of the tablet differs because of the way the SNAC absorption enhancer works, and the dosing schedule changes accordingly. More on that can be found on our semaglutide overview page.

Steady state, dose titration and why the first few weeks feel different

When you start Wegovy, the titration schedule (beginning at 0.25mg and stepping up roughly every four weeks) is not primarily about building efficacy. It is about giving your GI system time to adjust before steady state at each dose level is established. Full steady state at any given dose takes four to five half lives, so around four to five weeks. During that window, concentrations are still climbing each week, which partly explains why side effects like nausea tend to peak early and then ease as the body adapts.

Reaching the 2.4mg maintenance dose (or the 7.2mg dose approved by the MHRA in January 2026 for the higher-dose pen) does not mean concentrations keep rising indefinitely. Once the dose is stable, so are the blood levels, within a predictable band around the weekly peaks and troughs. A closer look at Wegovy's peak and half life across the titration schedule sets out those numbers dose by dose.

One quick habit worth building: mark your injection day in your phone calendar and set a weekly reminder. Because the half life smooths out missed-dose consequences compared with daily medicines, it can be easy to lose track of which day you injected. A 30-second calendar check is easier than working backwards from side-effect timing later. Details on the full dosing schedule are on our Wegovy treatment page.

How semaglutide's half life compares with other GLP-1 medicines

Semaglutide's seven-day half life is notably long within its drug class. Older GLP-1 receptor agonists such as liraglutide (found in Saxenda) have a half life of roughly 13 hours, requiring daily injections. Tirzepatide, the dual GIP/GLP-1 agonist in Mounjaro, has a half life of approximately five days, similarly long, supporting once-weekly dosing, though the two medicines work through partially different receptor mechanisms.

The question of how semaglutide's half life differs between Wegovy and Ozempic comes up regularly. The molecule is identical, what differs is the licensed indication and the doses used. Ozempic is licensed in the UK for type 2 diabetes, not weight management; presenting it as an alternative for weight loss would be outside its licence. For a visual comparison of concentrations over time, the semaglutide half life chart page maps the curve across the titration schedule.

If you are exploring weight-loss treatment options more broadly, our weight-loss treatment overview covers the licensed medicines currently available in the UK and what the clinical differences mean in practice. Treatment is a clinical decision, and the right starting point is a conversation with a prescriber who can review your full picture. Start your free consultation with our GPhC-registered prescribers whenever you are ready.