How Long Can I Leave Mounjaro Out of the Refrigerator? (October 2026)

01

How long can Mounjaro stay out of the fridge?

An in-use pen can stay out of the fridge for up to 30 days (not above 30°C). Keep Mounjaro pens in a fridge at 2–8°C and never freeze them.¹ Once in use, a pen can be kept out of the fridge not above 30°C for up to 30 days — useful for short trips — after which it should be discarded.¹

Two conditions sit inside that sentence. The pen must be in use, and the room must stay below the temperature limit. Miss either and the 30-day allowance no longer applies.

02

Which situation are you in?

Work out whether your pen is unopened or in use, because the rules differ.

03

What should I do now?

If your pen is in use and within the window, carry on and keep track of the date. If you are outside it, discard the pen safely using your sharps bin. If you cannot say how long a pen has been out, or how warm it got, treat it as uncertain and ask the pharmacy that supplied it before injecting.

Do not stretch the window to avoid waste. Medicine kept beyond the labelled limit is outside the tested conditions, so sterility and potency are no longer assured. If you need a new pen and are ready to continue treatment, you can view the current Mounjaro pen prices and consultation; the 2.5mg starting pen is £169.99 at the standard price, and all doses are in stock. For wider support on treatment, see our weight loss clinic.

Related guides: How long can you leave mounjaro out of the fridge and How long can mounjaro stay out of refrigerator and How long is mounjaro good out of the refrigerator and Can you leave mounjaro out of the fridge and Is it ok to leave mounjaro out overnight.

04 · Unopened vs in-use pens

Unopened pens versus in-use pens

The 30-day allowance applies only to a pen you have started. An unopened pen should be kept in the fridge and keeps until the expiry date printed on the box.¹

This matters because numbers circulate online that come from other countries' labels, and they do not match the UK product information. 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.¹

The patient information leaflet that comes in the box is the reference to keep to hand.¹³ If the leaflet and something you read online disagree, follow the leaflet.

Each pen contains four weekly doses.¹ A pen used on schedule is therefore finished well within the in-use window. The window matters most when doses are delayed or paused, because medicine left in a pen once the window ends should be discarded rather than used for a later dose.

05 · Heat, light and freezing

What happens if Mounjaro gets warm or freezes?

Warmth beyond the label limit takes the pen outside its tested range. The licence allows the pen to be out of the fridge only not above 30°C. Do not use a pen that has been above 30°C; contact the pharmacy rather than inject and hope.

Think about where heat sneaks in. A parked car on a sunny day, a windowsill, a bag left near a radiator or a hot-climate holiday can all push temperatures past the limit even when the house feels comfortable.

Freezing is a separate problem. The label is blunt: never freeze the pens, and never use a pen that has been frozen.¹ Hold luggage on a plane can also fall below freezing, which is why pens go in hand luggage.

Light is the third factor. Keep the pen cap on to protect it from light.¹ A pen sitting uncapped on a bright worktop is not storing as intended, even if the temperature is acceptable.

06 · Has my pen gone bad?

How to tell if Mounjaro has gone bad

Check both the pen's history and how it looks. Ask three questions: has it been frozen, has it been warmer than the label allows, and has the in-use window ended? A yes to any of them means the pen should not be used.

The solution in a genuine pen is clear and colourless; do not use a pen that looks cloudy or discoloured, has particles in it or is past its expiry. If anything seems different from that description, do not inject. Contact the pharmacy that dispensed it and describe what you have noticed.

A pen can look perfectly normal and still be past its window. Conversely, a pen that looks unusual is not a puzzle to solve yourself. Discarding a pen is an annoyance; injecting a compromised pen is a risk with no safety data behind it.

If you have used a pen you are unsure about and feel unwell, speak to a pharmacist or your prescriber. You can also report suspected side effects through the MHRA Yellow Card scheme.¹⁹

07 · Tracking the 30 days

How to track your in-use window

Write the date of first use on the carton or in your phone the day you start the pen. That one habit removes most of the guesswork. When the window ends, the pen goes in the sharps bin, whatever is left inside.

If you use the free GLPTrackr companion app for tracking a GLP-1 journey, you can log injection dates there as well. Either way, the aim is the same: to be able to say with confidence how long the pen has been in use.

Your usual injection day also matters. Mounjaro is injected under the skin weekly, on the same day each week, at any time of day, with or without food.¹ A regular routine makes it easy to see where a pen is in its life. If a dose is missed, the missed-dose rule applies: take it as soon as you can within 4 days (96 hours) of the scheduled time, and if more than 4 days have passed, skip it and carry on on your normal day.¹

Do not use the pen differently to stretch it out.

08 · Travelling and daily life

Travelling with Mounjaro and keeping it at home

You can fly with Mounjaro, and most holidays need no special arrangements. Carry pens in hand luggage, because hold luggage can fall below freezing, ideally in a cool bag with the prescription label or a copy of your prescription.¹ In-use pens tolerate up to 30 days not above 30°C. For hot climates, use an insulated pouch, and check destination rules for travelling with prescription injectables before you fly.¹

Unopened spare pens should stay in the fridge until needed.

At home, the simplest arrangement is a regular spot in the main fridge compartment, kept away from the freezer section.

Delivery follows the same logic. Our orders arrive by free next-day tracked delivery in temperature-controlled packaging, and same-day dispatch applies when you order by 3pm. Put unopened pens in the fridge when they arrive.

09 · Other medicines differ

Other medicines have their own rules

Storage limits belong to a specific medicine, so do not carry Mounjaro's numbers over to anything else. For any other product, read its leaflet or ask a pharmacist.

The same caution applies to advice that does not name a country. In the UK, an in-use pen can be kept out of the fridge not above 30°C for up to 30 days, and figures circulating online often come from other countries' labels.¹ If you are reading a forum or a social media post, check that it refers to the UK label before acting on it.

10 · Why storage matters

Why storage matters for your results

Treatment works gradually, so a pen that has lost potency is hard to spot. Because progress is slow and varies from person to person, a poorly stored pen could leave you wondering why a dose seems to do less than before, with no obvious cause.

Treating storage as part of the routine protects your investment and keeps your dosing predictable.

Mounjaro is a prescription-only medicine, supplied after an online consultation reviewed by a GPhC-registered prescriber, and used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice. If you are unsure about a particular pen, our support team can help Monday to Friday, 9am to 5pm, on 0333 207 0413 or at support@everydaymeds.co.uk.