What Happens If You Take Expired Semaglutide or an Out-of-Date Wegovy Pen

You're holding the pen, the date has gone, what's actually happening inside it?

Picture the scenario: injection day arrives, you reach into the fridge, and the date on the pen reads last month. The liquid looks exactly the same as it always has. Nothing smells off. The temptation to use it anyway is understandable, especially if your next supply hasn't arrived yet.

The problem is invisible. Semaglutide is a large peptide molecule, and peptides are sensitive to time, temperature and light in ways that small-molecule drugs are not. After the expiry date, chemical degradation accelerates: bonds break, the three-dimensional structure of the molecule changes, and what was a precise 2.4 mg dose may now be delivering a fraction of that. Less active medicine means less appetite suppression, less slowed gastric emptying, and potentially no meaningful effect on weight at all during that week.

There is also a subtler risk. Degraded peptides can form breakdown products whose behaviour in the body hasn't been studied in the way the intact molecule has. That doesn't mean a single expired injection causes a dramatic event, but the manufacturer's safety profile covers the medicine as it was formulated, not as it has since changed. Our frequently asked questions touch on related storage and handling queries if you want the broader picture.

The practical upshot: if you're asking what happens if you inject expired semaglutide, the most likely outcome is a week with diminished or absent therapeutic effect. That's not nothing, it disrupts your titration schedule and your progress tracking. It's also worth understanding what happens if you take too much semaglutide, since compensating for a weak dose by taking more is not a safe workaround. Beyond that, the unknowns are reason enough to skip the dose rather than use the pen.

How expiry and storage interact, because one accelerates the other

The date on a Wegovy pen is calculated assuming the pen has been stored correctly throughout: refrigerated between 2°C and 8°C, away from light, and not frozen. Once a pen is taken out of the fridge for travel or convenience, a separate clock starts. The SmPC sets a specific room-temperature window for in-use pens, the exact duration is in the Patient Information Leaflet and varies by product, so always check it rather than guessing.

What this means in practice: a pen that has spent several days at room temperature during a holiday, then been returned to the fridge, may have already lost meaningful potency before its printed date is even reached. If you want a detailed look at what expired Wegovy means for your treatment, that's covered in full separately. The expiry date and the storage rules work together; neither one overrides the other.

If you're ever unsure whether your pen has been stored correctly, treat it the same way you'd treat an expired one. Our Wegovy treatment overview covers the storage and administration basics that every patient should read before their first injection. And if a supply problem means you've had to stretch doses or skip a week, the question of timing flexibility around doses is worth understanding too, though specific guidance always comes from your prescriber and the leaflet, not general articles.

For context on what a legitimate pen looks like when it does arrive, at nume, your Wegovy ships from our GPhC-registered pharmacy via DPD with a tracking notification, in plain unbranded packaging, refrigerated in insulated packaging. The pen inside is sourced through the authorised UK supply chain. Seeing that chain clearly is part of knowing your medicine is genuine and within date.

The right thing to do with an expired or degraded pen

Skip the dose. That's the straightforward answer. Missing one weekly injection is far less disruptive to your treatment than using a pen that may no longer contain an effective dose, particularly if you're mid-titration. Your prescriber can advise on how to re-establish your schedule, the summary of product characteristics on the eMC contains the manufacturer's guidance on missed doses, and a prescriber-led review is always the right route for any titration question.

Dispose of the expired pen properly. Pre-filled injection pens are sharps waste; they go into a sealed sharps bin, not the general bin or recycling. If you want to understand more about using semaglutide after its expiration date in more detail, that's covered separately.

Then think about your supply. Running out or finding an expired pen at injection time usually points to a gap in ordering. Private treatment through a regulated pharmacy doesn't have to mean irregular supply, at nume, every repeat order goes through a clinician-led review before dispatch, and the process is designed so that re-ordering is straightforward rather than something you have to chase. If cost is a factor in how often you order, the real cost of Wegovy in the UK is worth reading before comparing providers, because what a transparent price includes matters as much as the headline number.

One final note: if you're currently on a different provider's supply and considering a transfer, or if you've had a gap in treatment, a fresh consultation is the right starting point. A prescriber can assess where you are in your journey before deciding the most appropriate next step. You can check your eligibility with our prescribers at any stage, no obligation, no pressure, just a proper clinical review.