How Long Does Mounjaro Last in the Fridge? (October 2026)

01 · The core answer

How long Mounjaro lasts: unopened versus in use

Unopened Mounjaro pens belong in the fridge at 2–8°C, and they keep until the expiry date printed on the box.¹ Once you start using a pen, the clock changes. A pen in use can be kept out of the fridge not above 30°C for up to 30 days, which is useful for short trips, after which it should be discarded.¹

The fridge is the right default for an unopened pen. Out-of-fridge storage is a convenience for pens you are already injecting from.

02 · Your next step

What to do with the pen in your hand

Check the printed expiry date first, then work out whether the pen has been started. If it has not, put it in the fridge in its original carton and leave it there until your next dose is due. If it has been started, note the first-use date so you know when the in-use period ends.

Each KwikPen contains four weekly doses, so a pen used on its normal weekly schedule is finished well inside the in-use limit.¹ The in-use limit matters mostly if you pause treatment or have a gap between doses. See our guide to how long an opened pen lasts for that situation.

If you are still deciding on treatment, our weight loss clinic explains how the process works. The Mounjaro pen starts at £169.99 per month for the 2.5mg starting dose (standard price, checked 24 October 2026), and every dose is in stock.

03 · Unopened pens

How long an unopened Mounjaro pen keeps in the fridge

Keep Mounjaro pens in a fridge at 2–8°C and never freeze them.¹ Unopened pens should be kept in the fridge and keep until the expiry date printed on the box.¹ There is no separate shorter window to remember for unopened pens stored correctly.

Store the pen in its original carton. The carton holds the batch number and expiry date.

Our dedicated page on unopened Mounjaro storage goes into more detail on this scenario.

04 · In-use pens

Storing a pen once you have started it

Once in use, a pen can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹ You may also keep an in-use pen in the fridge between doses. Either way, the 30 days is the limit for the pen once you have started using it, even if some medicine appears to remain inside.

Keep the pen cap on to protect it from light.¹

After 30 days (not above 30°C) in use, there is no tested basis for relying on the pen, so the sensible course is to dispose of it in a sharps container and start the next pen. For the specifics of a pen you are mid-way through, see how long a Mounjaro pen lasts.

05 · Freezing and heat

Freezing, heat and extreme temperatures

Never freeze Mounjaro, and never use a pen that has been frozen.¹ Discard it and contact your pharmacy for advice.

Heat is the other risk. The in-use allowance applies not above 30°C, so a hot car, a beach bag in full sun or a hot windowsill falls outside it. For hot climates, an insulated pouch is the sensible precaution.¹

Common storage mistakes include:

• Placing the pen where it could freeze.
• Leaving the pen in a bag in hold luggage, where temperatures can fall below freezing.
• Leaving the pen in a warm car or in direct sunlight.
• Leaving the pen without its cap on, which does not protect it from light.

If any of these happened, treat the pen as stored incorrectly and contact the pharmacy before injecting.

06 · Travel and delivery

Travelling with Mounjaro: luggage and airport security

You can fly with Mounjaro. 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 Check destination rules for travelling with prescription injectables before you fly.

In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements.¹ Travel tips that follow from this:

• Keep the pen in its original carton or with the pharmacy label so it is easy to identify at airport security.
• Keep the pen with you rather than checking it in.
• Use an insulated pouch in hot destinations, and keep it out of direct sunlight.
• Pack the sharps container or a travel-safe way to dispose of needles.

On the way to you, our pens travel in temperature-controlled packaging on free next-day tracked delivery. Put them in the fridge when they arrive unless you are about to inject. If a delivery sat out for a long time, contact us before using the pen. You can read more about how long Mounjaro lasts outside the fridge.

07 · Signs a pen has gone bad

How to tell if a Mounjaro pen has gone bad

A genuine UK Mounjaro pen comes from a registered pharmacy with a batch number and expiry date, arrives cold-chain packaged, and the solution inside is clear and colourless.¹ Look at the window before every injection.

Do not use a pen that has been frozen, looks cloudy or discoloured, has particles in it, is past its expiry, or has been out of the fridge for more than 30 days, or above 30°C in use.¹

If supply or packaging ever seems wrong, check the pharmacy on the GPhC register and contact the pharmacy before injecting. We are registered as GPhC 9012878 and supply genuine KwikPens through official LillyDirect supply. If you notice a side effect, you can report it through the MHRA Yellow Card scheme.¹⁹

08 · Leftovers and doses

Leftover Mounjaro, missed doses and dose counts

If you miss a dose, 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 one on your normal day.¹ Missing a dose does not change how long the pen can be stored; the in-use limit still runs from first use.

09 · Stored too long and in your body

Fridge life versus how long Mounjaro lasts in your body

These are two separate questions. Fridge life is about the pen. How long the medicine stays in your system is about tirzepatide, which has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system.¹ There is no way to speed this up, and nothing needs doing while it clears.

Our guides on how long Mounjaro lasts in your system and how long it lasts in the body cover that side. Storage does not change how long a dose acts once injected. It only affects whether the pen is still within the conditions it was tested for.

If you want a week-by-week view of what to expect as you begin, see the first-week storage and dosing guide. If you also use Wegovy, its storage rules differ, covered in our guide to Wegovy fridge storage.

10 · NHS supply

NHS and private supply: does storage differ?

No. Mounjaro is available on the NHS, but access is being phased in over several years.⁴ NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first.⁶

Whichever route you use, follow the leaflet in your box and the guidance from your prescriber. Our page on NHS Mounjaro fridge guidance covers that route specifically. Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber, and used alongside a reduced-calorie diet and increased physical activity. Individual results vary, and this page is information, not a substitute for medical advice.