Do weight loss injections need to be refrigerated?

Step 1: from the moment your pen arrives, keep it in the fridge

Your Mounjaro KwikPen or Wegovy pen is dispatched cold and should go straight into the fridge when it reaches you. The target is between 2°C and 8°C, which is the standard mid-shelf temperature in most household fridges. The door is warmer and less stable, the middle shelf or a dedicated drawer is better.

One practical check that takes under a minute: look at your fridge's temperature display (or pick up a cheap fridge thermometer) and confirm it sits in that 2–8°C window before you put your pen in. A fridge that's been nudged warmer by a summer heatwave or a packed weekly shop can drift out of range without you noticing.

Do not put the pen in the freezer. Frozen medicine should not be used. If your pen has accidentally frozen, keep it, do not inject, and call your prescriber or our pharmacist support team before doing anything else.

These are not rules we invented. The NHS medicines page for tirzepatide and the equivalent page for semaglutide both direct patients to follow the storage instructions in the Patient Information Leaflet exactly, because storage is one of the few things that can make an otherwise genuine pen ineffective.

Step 2: once you've used the first dose, the clock starts on room-temperature storage

Here is where most people have questions. After you've administered your first weekly injection from a pen, you don't have to put it back in the fridge for the remaining doses, but you can if you prefer. At room temperature, the pen stays usable for a limited window. The exact number of days differs between Mounjaro and Wegovy, and differs again from the Wegovy single-dose 7.2mg pen.

We deliberately don't print a specific number of days here, because the figures in your Patient Information Leaflet are the definitive source, and they can be updated. Check the leaflet that came in your box, it takes thirty seconds, and you'll see the exact room-temperature limit for your product and dose.

Room temperature means up to around 30°C. A pen left on a sunny windowsill in August, on a car dashboard, or next to a radiator can easily exceed that. Keep it somewhere genuinely cool, a bathroom cabinet away from the shower, a bedside drawer, or back in the fridge. Wherever you choose, keep the pen in its original carton with the cap on to protect it from light.

If you're weighing up which injection might suit your lifestyle and routine, our overview of weight loss injections in the UK covers both medicines side by side.

Step 3: know the situations where a pen should not be used

There are a handful of scenarios where the answer is simply: don't inject, and seek advice first. These include a pen that has been frozen and thawed, a pen left in a car or warm environment for a period that likely exceeded 30°C, and a pen where the liquid looks discoloured, cloudy or contains visible particles, Mounjaro and Wegovy should be clear and colourless to pale yellow.

Equally, check the expiry date printed on the carton. A pen past its date should not be used, even if it has been stored correctly the entire time.

If any of these situations apply, contact your prescriber before your next injection day rather than waiting. Injecting a compromised pen carries real risk, and replacing it quickly is the right move. Our frequently asked questions page covers some of the most common storage queries our team receive, and our prescribers are reachable seven days a week if you need a faster answer.

It is also worth knowing that a pen that has been correctly stored throughout its life is still a prescription medicine that must have been issued following a proper clinical assessment. If you're exploring options and want to understand which products have the strongest patient feedback, our guide to the best rated weight loss injections available through regulated UK services is a helpful place to look before you start a consultation. Our free consultation is the place to start, a GPhC-registered prescriber reviews your information the same day, not software.

Travelling with your weight loss injection pen

Travel is where storage anxiety tends to peak, particularly for anyone taking a longer flight or going somewhere warm. The practical answer: a small insulated cool bag with an ice pack keeps a pen within range for a journey. Most airline security policies treat pre-filled medical pens as essential medication; carry your prescription paperwork and the original packaging to avoid delays.

If you're crossing time zones, the day-of-week rhythm of your once-weekly injection matters less than the seven-day gap between doses. Your prescriber can advise on timing adjustments; don't change your schedule without checking first.

For international travel lasting more than a few days, check whether your destination has suitable refrigeration on arrival. Hotels almost always have a mini-fridge; self-catering accommodation is worth confirming in advance. A medication card in the local language is useful if you're travelling outside English-speaking countries.

How long you'll be on treatment is a separate conversation worth having with your prescriber before any long trip, and if you'd like to read about what BMI and eligibility criteria typically apply before treatment can be prescribed, our page on what BMI you need for weight loss injections sets out the clinical thresholds clearly. For broader background reading, our guide to the top rated weight loss injections currently available in the UK compares the options patients most commonly ask about, and our how long weight loss injections are typically taken page gives a grounded overview. And if cost is something you're thinking through, our weight loss injection pricing guide explains what a legitimate private price typically covers.