What happens if your Wegovy pen freezes — and what to do next

How freezing affects the medicine inside the pen

Semaglutide is a protein-based molecule in a liquid solution. Protein medicines are sensitive to temperature extremes in both directions: excessive heat degrades them, and freezing causes the proteins to aggregate or denature. The change happens at a molecular level, so the liquid can look perfectly clear after thawing and still be unsafe to use. There is no visual test that reliably confirms a frozen pen is undamaged.

This matters for your dose. If you are mid-titration on a GLP-1 treatment schedule, injecting from a compromised pen means your body receives less active medicine than intended, which disrupts the gradual escalation your prescriber has planned. It is not a situation that self-corrects the following week.

The NHS guidance on semaglutide storage confirms that a pen exposed to freezing temperatures should be discarded. If you are unsure whether your pen reached that threshold, the cautious and correct step is to treat it as compromised. A replacement pen from a verified source, reviewed by a prescriber, is the appropriate path. You can read the NHS's semaglutide medicine page for a patient-level summary of storage requirements: NHS guidance on semaglutide.

The one-minute check before you decide to discard

Before throwing anything away, take a moment to trace what actually happened. Hold the pen up to a light source and look at the solution. It should be clear and colourless, with no particles, cloudiness or discolouration. If you see any of those things, discard immediately. If the solution looks normal, that does not make the pen safe, it simply means you cannot rule anything out visually.

Next, consider where the pen was. Did it sit against the back wall of your fridge, where the temperature can drop below zero near the cooling element? Was it placed in a cool bag with ice packs touching it directly during travel? Did it spend time in a car boot in cold weather? A pen that stayed at the front of a shelf in a properly set refrigerator, away from the freezer compartment, has a low probability of having frozen. One that touched ice or spent hours in a frozen environment has almost certainly crossed the threshold.

That context (not the appearance of the solution) is the most useful piece of information to share with your prescriber. Our clinical team fields questions like this regularly; knowing the storage conditions helps them advise you clearly. For broader questions about your supply and costs, our Wegovy cost page explains what a genuine private prescription includes.

What to do if you believe the pen has frozen

Stop. Do not inject. The right sequence is: set the pen aside, note roughly how long it may have been exposed and at what temperature, then contact your prescriber. If you are an existing patient at a regulated pharmacy, that call or message should happen before your next scheduled injection day, missing one dose is far less disruptive than injecting from a damaged pen at the wrong point in your titration.

Your prescriber may ask you to skip that week's dose and pick up from the following week once a replacement arrives, or they may adjust the plan depending on how far into your titration you are. What they will not do is ask you to guess. The Patient Information Leaflet included in your box sets out the precise storage instructions and what to do if the recommended conditions have not been met, read it alongside any advice from your prescriber.

If you need to travel with Wegovy and are concerned about keeping it in range, the Mounjaro and Wegovy SmPCs on the electronic Medicines Compendium (eMC) detail the approved travel window and conditions; your prescriber can help you plan around a trip. For questions about what happens to your treatment progress after a missed or disrupted injection, our page on what to do if you miss a Wegovy shot covers the practical steps. And if you have ever wondered about the longer arc of the treatment, our guide on what happens after Wegovy is worth reading too.

Storing Wegovy correctly to avoid this happening again

Correct storage is simple once the habits are in place. Keep unused pens in their original box in the main body of the refrigerator, not in the door shelf (temperatures there fluctuate more) and not touching the back wall. Never place a pen in the freezer compartment, even briefly. When travelling, use a purpose-made cool wallet rather than loose ice packs that contact the pen directly.

Once a pen is in active use, room-temperature storage for a limited period is permitted, the exact duration is in the leaflet, and it varies by pen format. Do not exceed that window, and do not return a pen to the fridge after it has been stored at room temperature if the permitted period has elapsed. These are the conditions the manufacturer and the MHRA have validated; working outside them puts the medicine's integrity in question.

If you are new to Wegovy or still deciding whether it is the right option for you, our weight-loss treatment overview explains how it fits alongside other approaches. Questions about stopping treatment at any point are covered on our page about what happens if you stop Wegovy. And if you would like a prescriber to review your situation, including supply questions, start your free consultation and a GPhC-registered prescriber will read your answers the same day.