How long does a bottle of semaglutide last — and what affects it?

Why does the number of pens change month to month?

Wegovy is not supplied at a single fixed dose from day one. The licensed titration schedule begins at 0.25 mg weekly and steps up through 0.5 mg, 1.0 mg, 1.7 mg, and 2.4 mg, with each step typically lasting around four weeks. That means your first pen is a 0.25 mg pen, your second a 0.5 mg pen, and so on. The pens are not interchangeable; each one is calibrated to its own strength. You don't use more or fewer pens per month because of the escalation (you still go through one pen per month) but the pen itself changes as your dose increases.

Once you reach a maintenance dose, supply stabilises: one pen of that strength per month, every month, for as long as treatment continues. If your prescriber later adjusts your dose downward because of tolerability, you'd move back to a lower-strength pen. How long semaglutide continues to work is a separate question from supply, though the two are worth understanding together.

The 7.2 mg dose, approved by the MHRA in April 2026, is available as a dedicated single-dose pen, one injection per week, one pen per month, same pattern. Your prescriber confirms whether that dose is appropriate for you based on your response at the standard maintenance dose.

Does leaving a pen out of the fridge use it up faster?

Not in the sense of doses, no, a pen still contains four doses regardless of how it's stored. But storage conditions do affect whether those doses remain usable. Wegovy pens must be kept in the fridge (2°C to 8°C) until you're ready to use them. There is a permitted window for keeping a pen at room temperature once it's been removed from the fridge, but that window has a specific duration you should check in your Patient Information Leaflet rather than rely on a round number you've read online. The leaflet that comes with your pen, and the full prescribing information on the eMC (Electronic Medicines Compendium), give the exact figures.

In practical terms: most people keep their current pen in the fridge door and only take it out shortly before each weekly injection. That keeps things simple. If a pen has been left out longer than the permitted period, it should not be used, contact your prescriber or pharmacist. Wasted doses are a real consideration, which is one reason clinical oversight across every repeat matters.

Injection sites also don't change supply duration, though rotating between the abdomen, thigh and upper arm as directed is worth mentioning because it protects the injection sites themselves over months of treatment.

How does the escalation schedule affect the overall length of treatment?

Reaching 2.4 mg from the starting dose takes roughly five months if every step goes to plan, one month at each rung of the ladder. That's five different pens before you're on the standard maintenance dose. Some people tolerate the escalation quickly; others need to spend longer at an intermediate dose. Your prescriber reviews progress before authorising each repeat, which is why when Wegovy starts working matters practically, it shapes whether continuing makes sense.

NICE's appraisal of semaglutide (TA875) recommends a review after six months on the maintenance dose: if weight loss is below 5% of starting body weight, the clinical case for continuing is weaker and a prescriber should discuss this with you. That built-in review point is another way supply duration becomes a clinical question rather than a simple arithmetic one.

If you're considering the private route and want to understand how Wegovy is priced across a full course, that context is worth reading alongside supply logistics. Costs compound across months, especially during the dose-escalation phase, and knowing what each supply cycle includes helps you plan.

What happens if you miss a dose, does the pen last longer?

A pen contains four doses whether you use them weekly or not, but missing doses is not a way to extend supply usefully. Semaglutide's half-life means it stays active in the body for several days after each injection (how long it stays in your system is a question worth reading up on separately) but the clinical benefit of consistent weekly dosing is well established, and gaps can affect how well treatment works.

If you miss a dose and your next scheduled injection is more than five days away, the Patient Information Leaflet advises you can take the missed dose then. If it's less than five days away, skip it and continue as normal. Either way, you still have the remaining doses in the pen. What you should not do is take an extra dose to compensate. For anything beyond that, the honest answer is: ask your prescriber. A question our prescribers hear most weeks is about timing after a missed injection, it's worth raising rather than guessing.

For a fuller picture of how the medicine behaves over time, the page on how long semaglutide lasts in the body covers the pharmacology side in plain language.