How long does Wegovy last in your system — and how long do the effects last?

Step 1: how long semaglutide stays active after each weekly injection

Semaglutide has an elimination half-life of around seven days. In practical terms, that means each weekly dose overlaps with the tail of the previous one, keeping a relatively steady level in your bloodstream. It takes approximately five half-lives (so roughly five weeks) for semaglutide to fall to negligible levels after you stop injecting entirely.

That long half-life is actually part of the design. It smooths out the peaks and troughs you'd get with a daily medicine, which is why most people don't notice a dramatic difference between, say, injection day and the day before their next dose. If you're curious about how long semaglutide lasts and what that means for your weekly dosing schedule, that's covered in more detail elsewhere, but for most people the practical question is the one below.

The NHS medicines information for semaglutide sets out the full pharmacology, and it is worth knowing that the five-week clearance window also informs guidance around conception and stopping treatment.

Step 2: how long before the effects actually kick in, and when they peak

This is the part that catches people off guard. The drug may be present from week one, but the weight-loss effects accumulate gradually. Wegovy's licensed titration schedule starts at 0.25 mg and steps up roughly every four weeks until you reach the 2.4 mg maintenance dose. That process alone takes about sixteen to twenty weeks.

The STEP 1 trial, published in the New England Journal of Medicine, followed adults with obesity for 68 weeks. Average weight reduction at the 2.4 mg dose was around 15% of body weight. Most of that loss occurred progressively across the full trial period, not in a single burst at the start. A newer 7.2 mg dose (approved by the MHRA in early 2026) showed around 20.7% average weight loss over 72 weeks in trials, narrowing the gap with tirzepatide.

You might feel reduced appetite within the first few weeks, particularly around dose increases. Visible weight change tends to follow. If you want a more granular look at how long Wegovy takes to work in week-by-week terms, that page breaks the timeline down further. The honest answer is that this medicine rewards patience more than most.

Step 3: how long Wegovy lasts as a treatment, and what happens when it stops

Here's the thing many people aren't told clearly enough at the start: Wegovy's effects last as long as you take it. The NICE technology appraisal for semaglutide (TA875) recommends it for a maximum of two years within specialist weight management services on the NHS. Private prescribing follows the licensed indication, and your prescriber will review your treatment at each repeat.

When treatment stops, the physiological effects unwind. Appetite signalling returns towards its previous baseline, and weight regain is common. A large extension study of the STEP 1 cohort found that participants regained about two-thirds of their lost weight within a year of stopping. That is not a failure of willpower, it reflects how weight regulation biology works. If you're weighing up what Wegovy costs as an ongoing private treatment, factoring in the long-term nature of the medicine is part of that picture.

Stopping Wegovy is genuinely a clinical conversation. Our prescribers review this at every repeat, and if you have concerns about how your treatment is going, our team is reachable seven days a week.

After opening: how long a single Wegovy pen stays usable

Once a Wegovy pen has been started, it has a limited window at room temperature. The exact number of days is stated in the Patient Information Leaflet and on the NHS semaglutide medicines page, always check the leaflet that comes with your pen, because the window for the new 7.2 mg single-dose format may differ from the multi-dose pens. Before opening, pens are stored in the fridge between 2°C and 8°C. For the full storage detail, this page covers how long an opened Wegovy pen remains usable, and if you want to understand how long a Wegovy shot lasts once it has been administered, that is covered separately.

The practical upshot: keep your pen in the fridge, don't freeze it, check the leaflet for the in-use window, and if you're ever unsure whether a pen is still good, speak to your prescriber or pharmacist rather than guessing.

If you'd like a prescriber to assess whether Wegovy is the right fit for where you are right now, speak to our prescribers through a free consultation, reviewed the same day by a GPhC-registered Independent Prescriber, not a bot.