Semaglutide shelf life after opening: what happens to your Wegovy pen

Step 1: what changes the moment you use your first dose

Before a Wegovy pen is opened, it travels in a supply chain kept at 2–8°C and carries a use-by date printed on the label. The moment you dial your first dose and inject, the pen enters a different phase. Room-temperature storage now applies, and a separate, shorter deadline kicks in. That deadline is printed in your Patient Information Leaflet, the leaflet that comes in the box, not a third-party source. The exact figure can vary between product batches and updated leaflet versions, so the PIL is always the authority.

The practical reason for this change is straightforward. Biological medicines like semaglutide are stable under refrigeration for months, but exposure to ambient warmth, light fluctuations, and repeated handling accelerates degradation. The licence-holder has tested exactly how long the opened pen stays within specification at normal room temperature, and the PIL records that result. Unopened pen storage follows a different set of rules entirely, so the two should not be confused.

One thing that catches people out: if you start a new pen mid-month (perhaps because a dose was delayed over a bank holiday) the clock on that pen begins at first use, not at the date it arrived. A pen sitting partly used on the shelf does not reset.

Step 2: keeping the opened pen in the right conditions

Once in use, keep your pen at room temperature, below 30°C, away from direct sunlight and heat sources such as radiators or car dashboards. Do not put it back in the fridge. Repeated temperature cycling (warm, then cold, then warm again) is harder on a biological medicine than stable room-temperature storage, and the product is not licensed for that pattern of handling.

The NHS guidance on semaglutide covers storage requirements and is worth reading alongside your PIL; the NHS semaglutide medicines page sets out the key handling points in plain language. Keep the pen in its original packaging where possible (the cardboard sleeve offers some light protection) and store it somewhere stable rather than in a bag that moves between warm and cool environments throughout the day.

Never use a pen that has been frozen. Freezing irreversibly damages the solution, and there is no visual way to tell that harm has occurred. If a pen has been accidentally frozen, treat it as unusable and contact your prescriber or pharmacy before injecting.

Step 3: what to do if a dose falls outside the window

If you realise an opened pen has passed its in-use deadline before you have used all four doses, do not inject from it. The remaining doses are no longer covered by the product licence and should not be used. Dispose of the pen in a sharps container and contact your prescriber to discuss next steps, whether that is a replacement pen or a brief interruption in treatment.

The same applies if you are genuinely uncertain how long a pen has been open. If you cannot confidently place when you first used it, treat it as potentially outside its window. This is one of those situations where precision matters: semaglutide's effectiveness depends on receiving an intact, stable dose at each injection. A degraded pen may deliver less active medicine than the label states, which can affect both results and tolerability.

For a fuller picture of how long Wegovy pens last across the full treatment journey, the Wegovy shelf life guide covers both unopened and in-use pens together. If you are thinking about longer-term questions such as how long treatment continues, that is a conversation worth having with a prescriber rather than drawing conclusions from storage timelines alone.

Wegovy shelf life once opened: the questions our prescribers hear most

A question that comes up regularly: can you use a dose from an opened pen if the injection date slips by a day or two? The answer on scheduling is in your PIL, the accepted window around a missed weekly dose is specified there, and for anything beyond that a prescriber's guidance takes precedence. What the PIL does not do is extend the pen's overall in-use period. The two deadlines are separate: one governs when in the week you can inject, the other governs when the pen is still fit to use at all.

Another common query concerns travel. If you are going away and your pen is already open, keep it in your hand luggage (not the hold, where temperatures can drop sharply) and carry it in an insulated pouch if the destination is hot. Airport security recognises medical injection devices; carry your prescription documentation. For a more detailed breakdown of in-use storage across different situations, including travel and warm weather, that dedicated page covers the specifics.

Understanding how semaglutide behaves in the body can also help put shelf life in context: the medicine has a long half-life in the bloodstream, which is why once-weekly dosing works. But that pharmacokinetic stability inside the body is separate from the chemical stability of the medicine sitting in a pen at room temperature. The two should not be conflated.

If you have questions about managing your Wegovy treatment or your pen has been handled in a way you are unsure about, speak to our prescribers, they review patient queries seven days a week and can advise on the safest course of action. Patients sometimes raise wider health questions during these conversations too, including whether Wegovy can cause ovarian cysts, and our team can help you weigh up any concerns like that alongside your treatment plan.