Wegovy expiry after opening: the rules, the risks, and what most people get wrong

The biggest misconception: the outer expiry date is not your in-use deadline

Many people glance at the date stamped on their Wegovy carton, see it is months away, and assume the pen is fine to use. That date tells you the pen is safe to use up to that point only if it has been stored correctly and has not yet been opened or used for the first time. Once you start using it, a different clock begins.

The Wegovy pen contains a liquid solution of semaglutide. Like most biological medicines, semaglutide in solution is stable for a defined period once it is out of consistent refrigeration. The Wegovy Summary of Product Characteristics on the eMC sets out the exact in-use period, refer to that document or the leaflet in your box for the precise figure, because the window can differ between product versions and any updated guidance takes precedence over general summaries.

The practical point is this: the carton date and the in-use period are two separate things, and our guide to Wegovy expiry explains how to read both correctly so you are never relying on the wrong one. Confusing them is one of the most common storage errors our prescribers hear about, and it is entirely understandable given how expiry labelling usually works on everyday medicines.

Room temperature versus the fridge: why it changes the window

Unused Wegovy pens should be kept refrigerated between 2°C and 8°C. At those temperatures, the medicine is stable up to the printed expiry date. Once the pen is out of the fridge and being used, it can typically be kept at room temperature for a limited period, again, the Patient Information Leaflet gives the verified figure, and you should follow it to the letter rather than relying on approximations from any secondary source, including this one.

A practical tip worth knowing: keep your current pen in a consistent, cool part of the room rather than somewhere that gets warm, a bag left in a hot car, for example, or a windowsill in direct summer sun. Heat accelerates degradation even within the stated window. Many people tuck their in-use pen into the fridge door alongside other everyday items, which works well as long as it stays above 2°C and away from the freezer compartment. Frozen semaglutide solution should not be used.

For a more detailed breakdown of where and how to keep your pens, our guide on how to store Wegovy after opening covers refrigeration, travel and what to check before each injection, and our dedicated wegovy storage after opening page goes further on the specific conditions to maintain once the pen is in use.

What happens if the in-use window has passed?

The short answer is: do not inject from a pen that has exceeded its in-use period. Semaglutide that has been outside appropriate storage conditions for too long may have reduced potency, which means your weekly dose could be delivering less medicine than intended. This matters because consistent dosing is part of how the treatment works, irregular or sub-therapeutic amounts can undermine results and make side-effect patterns harder for your clinical team to interpret.

There is also no reliable way to tell whether a pen has degraded by looking at it. The solution may appear unchanged. Checking the pen visually before each injection is still worth doing (the NHS semaglutide medicines page advises not to use the injection if it looks cloudy, discoloured or contains visible particles) but a clear-looking solution does not confirm potency after the window has passed.

If your pen has expired or you suspect it has been stored outside the recommended range, the right step is to dispose of it safely using an approved sharps container and contact your prescriber before your next dose. Do not skip a dose without guidance; your prescriber can advise whether you should restart the same dose or adjust.

Keeping track: a practical approach

Tracking in-use dates is simpler than it sounds. Write the date you first used each pen on a small piece of tape stuck to the barrel, or add a phone reminder for the day the in-use window closes. Knowing that date in advance means you are never caught short on injection day wondering whether the pen is still within its usable period.

If your treatment schedule changes, say because you are travelling or have had a break in supply, the rules around restarting and pen validity are worth clarifying with your prescriber rather than estimating. Any questions about your specific prescription are best put to a clinical team who knows your full history. You can reach our aftercare team seven days a week for guidance between consultations.

For context on how Wegovy compares with other licensed weight-loss options in the UK, the treatment overview sets out what is currently available and how each works. And if you have ever wondered how Wegovy's semaglutide relates to Ozempic, there is an important licensing distinction worth reading before drawing any comparisons.