Does Wegovy go off — and how can you tell?

You've found a pen, here's the first thing to do

Picture this: you're clearing out the cool bag from a holiday, or you pull a pen from the back of the fridge door and realise it's been there longer than you thought. The immediate question is whether it's still usable. The single most useful habit is also the quickest, turn the pen over and read the expiry date printed on the label. That check takes about fifteen seconds and tells you the most important thing straight away. If the date has passed, the pen should not be injected. The manufacturer cannot guarantee the potency or safety of semaglutide beyond that point, and using an expired pen risks receiving less than the intended dose at exactly the moment you were expecting reliable treatment.

Expiry dates on Wegovy pens are set based on stability testing conducted under controlled storage conditions. When a pen has been kept correctly (refrigerated at 2–8°C throughout its life) the medicine remains stable up to that printed date. When storage has drifted outside those conditions, potency may fall earlier, which is why our page on whether Wegovy goes bad is worth reading alongside the date alone, because it covers how storage conditions affect the medicine's integrity before that deadline is even reached.

Our FAQs page covers a range of practical questions about starting and maintaining treatment, including what happens when doses are delayed.

What poor storage actually does to semaglutide

Semaglutide is a peptide (a protein-based molecule) and peptides are sensitive to heat, light and physical stress in ways that a paracetamol tablet is not. Leaving a Wegovy pen on a sunny windowsill, in a hot car, or in a bag pressed against a radiator can begin to degrade the active molecule even if the pen is several months inside its expiry date. The medicine may look identical, but its biological activity can be reduced.

Equally, freezing does damage. A pen that has been accidentally frozen (perhaps placed against the back wall of a fridge set too cold, or left in a car overnight in winter) should not be used. Ice crystal formation disrupts the solution in ways that cannot be reversed by thawing. The NHS medicines page for semaglutide confirms that frozen pens must be discarded.

Once a Wegovy pen is taken out of the fridge for use, it may be stored at room temperature for a defined period. That window differs depending on the pen format and is set out precisely in the Patient Information Leaflet that comes in the box, always check that leaflet rather than relying on a number you have read online. If you are unsure whether your pen has been out of the fridge for too long, the patient-safety answer is to contact your prescribing team before injecting. For questions about whether semaglutide goes off in a broader sense, that page covers the active ingredient across different formats.

Visual signs that a pen should not be used

Even a pen that is in date and appears to have been stored correctly deserves a visual check before each injection. Wegovy solution should be clear and colourless to slightly yellow. It should be free of particles and should not look cloudy or milky. If you hold the pen up to a good light source and notice any of the following, do not inject it: cloudiness or haziness in the liquid, visible floating particles or clumps, or a colour that looks darker than pale straw yellow.

These are signs that the protein structure of semaglutide may have been compromised. The change could stem from temperature excursions, from the pen having been dropped and shaken vigorously, or occasionally from a manufacturing defect. None of those can be ruled out by looking at the packaging alone. If in doubt, contact your pharmacist. Suspected product quality problems with any medicine can also be reported through the MHRA's Yellow Card scheme, which exists precisely for issues like this.

For readers who want to understand how treatment changes over time and what happens as doses increase, our page on what Wegovy goes up to sets out the full licensed dose pathway.

What to do with a pen you cannot use

A pen that has expired, been exposed to incorrect temperatures or failed a visual inspection should not be thrown into the household bin. Sharps (including used and unused pens) are clinical waste. Your dispensing pharmacy can advise on local sharps disposal routes; many community pharmacies accept them. Keeping a dedicated sharps container is the tidiest solution if you are on ongoing treatment.

If your current prescription has been disrupted because of a pen you cannot use, the right step is to contact your prescriber before attempting to adjust your schedule. Skipping or delaying doses, or doubling up, is not a decision to make without clinical input. Our page on how to come off Wegovy is relevant if you are thinking about pausing treatment rather than simply replacing a pen. And if you want to understand the longer arc (how the medicine's effect evolves over months) the page on when semaglutide wears off addresses that question directly.

If you are not yet on Wegovy and are weighing up whether it might be right for you, a free consultation with one of our prescribers is the practical next step. There is no algorithm involved, a GPhC-registered clinician reads your answers the same day. Check your eligibility and start your free consultation here.