What Happens If Your Wegovy Gets Warm (and When It's Still Safe to Use)

The biggest misconception: if the liquid still looks clear, the pen is fine

This is the question our prescribers hear most weeks in some form: the pen sat in a warm car, a sunny bag, or on the kitchen counter overnight, it looks exactly the same as before, so surely it's still good to use?

Not necessarily. Semaglutide is a protein-based molecule, and proteins degrade when exposed to heat. The degradation is chemical, not visual. A pen that has overheated won't turn cloudy, change colour, or smell different. It will simply look like a normal pen while potentially delivering a weakened or unstable dose. That's the problem with relying on appearance alone.

The same applies to freezing. If a Wegovy pen has been frozen (say, pushed to the back of the fridge where the temperature drops below 0°C) the medicine should be considered compromised and the pen discarded. Neither heat damage nor freeze damage is visible to the naked eye.

The NHS guidance on semaglutide confirms that pens must be stored refrigerated at 2–8°C, and that specific room-temperature limits apply once a pen has been removed from the fridge. Those limits are set out in the NHS semaglutide information and in the full Patient Information Leaflet included with your pen. The Leaflet is the authoritative reference, follow it precisely, not a general estimate found online.

What actually happens to semaglutide when it gets warm

Wegovy contains semaglutide, a GLP-1 receptor agonist manufactured as a sterile solution for injection. Like all biological medicines of this type, it is temperature-sensitive by nature. At refrigerator temperature, the molecule remains stable for its licensed shelf life. Above that range, molecular activity accelerates and the structure of the protein can begin to change, a process called denaturation.

This matters practically because a partially degraded pen may deliver less active medicine per dose than it should. You might experience reduced appetite suppression or less effect than you'd previously noticed, and if you're curious about what happens if you stop Wegovy altogether, that's a separate but related question worth understanding. You won't necessarily feel any different immediately after the injection itself, which makes it easy to unknowingly carry on with a compromised pen for weeks.

There is also a safety dimension. Injecting a degraded biological medicine carries a small but real risk of an unexpected reaction. This is part of why manufacturers set conservative storage limits and why pharmacists are direct about discarding exposed pens rather than taking a chance.

For context on the broader considerations around your treatment (including what changes between doses) the Wegovy overview at nume covers the essentials clearly.

Room temperature: what the rules actually say

Wegovy pens can be kept at room temperature for a limited period once removed from the fridge, this is an intentional allowance built into the licence for real-world practicality. The permitted window and maximum temperature are stated precisely in the Patient Information Leaflet and on the eMC (the Electronic Medicines Compendium, where UK prescribing information is published). That window is not reproduced here because summarising it imprecisely could cause harm; the Leaflet's wording is the one to follow.

What the rules do not allow: a pen that has exceeded either the time limit or the temperature ceiling during that window. If you're uncertain whether it has, the conservative and correct answer is to treat it as expired and request a replacement. This is not wasteful caution, it reflects how these medicines are licensed and dispensed.

If you're weighing up the practical costs of replacing a pen, the Wegovy pricing guide at nume explains what a private prescription typically involves, so you're not caught off guard. And if you're wondering about a missed dose in the same situation, there's guidance on what to do if you miss a Wegovy shot that covers the clinical thinking.

Practical steps if your pen has been in the heat

First: don't inject it yet. Check the Patient Information Leaflet for the exact room-temperature allowance and compare that against how long and how warm the pen was exposed. If you're confident it was within limits, it is likely fine. If you're not sure, that uncertainty is your answer.

Contact a pharmacist (any registered pharmacy, not just the one that dispensed it) or your prescriber. Describe the situation honestly: what temperature, roughly how long, and whether the pen had already been used (partially used pens have different considerations from sealed ones). They can advise whether to proceed or request a replacement. It's also worth reading about what happens after Wegovy if this incident prompts you to think longer-term about your treatment plan, and separately, many patients find it useful to understand what happens when you get off Wegovy so they can make fully informed decisions going forward.

Disposing of a pen you're not going to use: use a sharps container. If you don't have one, a 1-litre sharps container is a straightforward solution, and local councils provide sharps collection. Never put a pen in a household bin.

Going forward, a few habits help: keep pens in the main body of the fridge, not the door (door temperatures fluctuate more). When travelling, an insulated cool bag with an ice pack is worth the minor inconvenience. If you're flying, carry pens in your hand luggage, aircraft hold temperatures are unpredictable. The nume FAQs include practical storage questions that come up regularly. If you have ongoing concerns about your treatment, our support team is available seven days a week.

For anyone reassessing their treatment after an incident like this, speaking directly with a prescriber is the right move. Speak to our prescribers through the free consultation, same-day clinical review, no waiting list.