How Long Can Mounjaro Stay Unrefrigerated? UK Guide (October 2026)

01 · The core answer

The short answer: in-use pens get 30 days (not above 30°C), unopened pens need the fridge

An in-use Mounjaro KwikPen can live out of the fridge for up to 30 days, provided it stays below the temperature limit on the label. Once in use, a pen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away.¹ The 30 days start from when you first use the pen.

Unopened pens are different. Store them in the fridge at 2–8°C and never freeze them. They keep until the expiry date printed on the box, as long as they have been stored properly.¹³

You will see other figures online. Many come from other countries' labels, which are not the UK licence. For a UK-supplied KwikPen, the UK leaflet and the pharmacy that dispensed it are the right sources.

02 · Which applies to you?

Which situation are you in?

If your question is about the fridge side, see how long a pen can stay in the fridge.

03 · What next?

What to do next if a pen has been out

Start with the plain facts: is the pen unopened or in use, how warm did it get, and has it ever been near freezing? An in-use pen that has been at ordinary room temperature, within the 30-day limit, is working within its licence. An unopened pen that has spent time outside the fridge is a question for the pharmacy: check with them before using it rather than relying on a remembered day limit.

If you are a customer, contact our support team (Monday–Friday 9am–5pm) at support@everydaymeds.co.uk or on 0333 207 0413 with the pen's details. If you are thinking about starting treatment, our Mounjaro pen page shows current doses, with the 2.5mg starter pen at £169.99 per month at the standard price, and our weight loss clinic explains how treatment works.

Related guides: How Long Does Mounjaro Stay In Your System - UK Guide and How long does mounjaro last unrefrigerated and How long does mounjaro stay in your body.

04 · In-use pen rules

How storage works for an in-use pen

An in-use pen is one you have started injecting from. Each KwikPen contains four weekly doses.¹ Over that time you have two valid options: keep the pen in the fridge between doses, or keep it at room temperature below the label's limit for up to 30 days (not above 30°C).

Neither option is better for the medicine, provided you stay within the licence. The fridge is simply easier for most households because you never have to think about the clock. Room-temperature storage is handy for people who travel for work, who want the pen with them, or who find a cold injection uncomfortable.

The 30-day figure is a ceiling, not a target. A pen that has done its four doses is finished. A pen that has reached the limit without finishing its doses should be discarded, which is exactly what the licence says: after that period it should be discarded.¹

Practical habits that make the limit easy to respect:

• Write the first-use date on the carton when you take the pen out for the first time.
• Keep the pen cap on between injections, which protects it from light.
• Keep the pen in its carton at home, away from radiators, windowsills and cars.
• Check the pen before each injection and never use one that has been frozen.

05 · Unopened pens

Unopened pens: why the fridge matters

Unopened pens should be kept in the fridge until first use and keep until the expiry date printed on the box.¹ The recommended range is 2–8°C, and pens must never be frozen.¹³

You may find confident statements online giving an exact number of days that an unopened pen survives out of the fridge. If an unopened pen has been out of the fridge, check with the pharmacy before using it rather than relying on a remembered day limit, because figures circulating online often come from other countries' labels.¹

That advice protects you from two mistakes. The first is assuming a pen is fine because it looks normal. Tirzepatide in solution does not announce damage with a visible change you can rely on. The second is assuming a pen is ruined and throwing away a perfectly usable one. The pharmacy can look at the circumstances, including how long it was out and roughly how warm it was, and give a clear answer.

Store spare pens at the back of the main fridge compartment rather than the door, where temperature swings are largest, and away from the freezer compartment or the cooling element, where pens can freeze.

06 · Warm and frozen pens

What happens if Mounjaro gets warm or freezes?

A pen that has been warmer than the label allows is outside its tested window, which means sterility and potency are no longer assured. It means nobody can vouch for the dose it delivers or for how clean its contents remain, so the safe choice is not to inject from it and to ask the pharmacy.

Warm exposure usually happens in ordinary ways: a pen left in a parked car, in a bag on a sunny windowsill, next to a radiator, or in a rucksack on a hot day. If you realise a pen has been somewhere hot, take it out of the heat, keep the carton, and note roughly how long it was there. That detail helps the pharmacy advise you.

Freezing is a separate problem and the rule is absolute: never use a pen that has been frozen.¹ Freezing happens at the back of an over-cold fridge, next to an ice pack in a cool bag, or in hold luggage on a flight, where temperatures can fall below freezing. A pen that has frozen and thawed may look completely normal and still be unusable.

Do not try to rescue a doubtful pen by re-chilling it, shaking it or warming it in your hands. Contact the pharmacy, explain what happened, and let them advise whether a replacement is appropriate.

If you notice anything unexpected after an injection and you are not sure the pen was stored correctly, speak to your prescriber. You can also report suspected problems with a medicine through the Yellow Card scheme.¹⁹

07 · Travelling with pens

Travelling with Mounjaro

You can fly with Mounjaro, and for most holidays you do not need special arrangements. In-use pens tolerate up to 30 days (not above 30°C) below the label's temperature limit, so a typical trip fits within that window.¹

The most important rule is to carry pens in hand luggage. Hold luggage can fall below freezing, and a frozen pen cannot be used. Ideally pack the pen in a cool bag with the prescription label or a copy of your prescription, and check destination rules for travelling with prescription injectables before you fly.¹

For hot climates, use an insulated pouch rather than a bare bag. Keep it out of direct sun, out of parked cars and away from beach bags that sit in full light. If you are carrying spare unopened pens for a long trip, keep those cool as well, because unopened pens belong in the fridge until first use. At your destination, put them in a fridge if one is available.

A few practical travel habits help:

• Plan your injection day around the trip so you are not injecting in a rush at the airport.
• If your injection day falls during travel, you can change your weekly injection day provided there are at least 3 days between two doses.¹
• Pack your sharps disposal approach in advance; do not put used needles in general rubbish.
• Keep the pen in its carton so the cap and labelling stay with it.

If you miss a dose while away, take it as soon as you can within 4 days (96 hours) of the scheduled time; if more than 4 days have passed, skip it and take the next dose on your normal day.¹

08 · Delivery and cold chain

Your delivery: how long can a pen stay in the box?

A delivered pen should go into the fridge as soon as you open the parcel, unless you are about to start using it. Our orders travel in temperature-controlled, discreet packaging with free next-day tracked delivery, and same-day dispatch applies when ordered by 3pm. The point of that packaging is to protect the pen on its journey, not to act as storage at home.

If you cannot be home, ask someone to take the parcel in or use the tracking to plan around the delivery. A parcel left on a sunny doorstep or in a hot hallway is the sort of situation worth avoiding. If a delivery is delayed and the pen arrived warm, contact support before using it. Our separate guide on how long Mounjaro can stay in its delivery box goes into the practicalities.

Once the pen is unpacked, check the following before putting it away:

• The box and label match your prescription and dose.
• The expiry date printed on the box is in the future.
• The pen looks undamaged and the cap is on.

Then store it at 2–8°C if it is unopened. Our team can help if anything looks wrong, as can the patient information leaflet supplied with the pen.¹³

09 · Common storage mistakes

Common storage mistakes and how to avoid them

Most storage errors come from habit rather than ignorance.

Treating the 30-day limit as flexible. The limit is part of the licence. Past it, the pen should be discarded.¹ Using a pen beyond that window, or squeezing extra doses from leftovers, is outside the licence.

Not marking the first-use date. If you cannot remember when you started a pen, you cannot prove it is inside the window. Writing the date on the carton takes seconds.

Leaving the cap off. Keep the pen cap on to protect it from light.¹ Light protection matters for in-use pens that live at room temperature.

Using the fridge door. The door is the warmest, most variable spot. The back of a main shelf is steadier.

Freezing by accident. Ice packs placed directly against a pen, or a pen pushed against the back wall of an over-cold fridge, can freeze it. If you suspect freezing, do not use it.

Trusting a remembered figure. Day limits from forums, social media or another country's label can be wrong for a UK KwikPen. Check the UK leaflet or ask the pharmacy.

Assuming a pen that looks fine is fine. Appearance is not a reliable test of whether a pen has been stored properly.

10 · Other GLP-1 pens

Does the same rule apply to Wegovy, Ozempic and other pens?

No, you should not assume it does. Each medicine has its own licence, and the in-use period and storage limits are set separately for every product.

For Wegovy, use the Wegovy leaflet and read our guide on how long Wegovy can be unrefrigerated, which covers its storage rules in their own right.¹⁸ For Ozempic or any other injectable, read the leaflet in your box. Ozempic is semaglutide licensed for type 2 diabetes — it is not a UK weight-loss medicine. It is also worth knowing that insulin has its own storage instructions, and none of the Mounjaro rules apply to it. If you take insulin or a sulfonylurea alongside Mounjaro, your doses may need adjusting because of the risk of low blood sugar, so speak to your prescriber.

The exact numbers are not interchangeable, and you should not borrow one product's figure for another.

11 · Storage and your treatment

Storage, dosing and what stays in your body

Storage matters because the dose you inject has to be the dose you intend. Mounjaro is injected once a week under the skin, on the same day each week, at any time of day, with or without food.¹ Everyone starts on 2.5mg once a week. After at least 4 weeks the dose can step up, depending on how you respond and tolerate it, up to a maximum of 15mg weekly.

If a pen is spoiled and you have to skip or delay a dose, the missed-dose rule applies: take it as soon as you can within 4 days (96 hours), otherwise skip it and carry on on your usual day, never taking two doses within 3 days of each other.¹ A short gap while the pharmacy sorts a replacement is far safer than injecting from a pen you cannot trust.

You may also be wondering how long the medicine remains active after your last dose. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system, and nothing needs doing while it clears.¹