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

01 · The short version

The two storage clocks for a Mounjaro pen

A Mounjaro pen has two separate limits, and mixing them up is the commonest storage mistake. Unopened pens are governed by the expiry date on the box. In-use pens are governed by a 30-day limit that starts the day you first inject from them.¹

Day limits for unopened pens that circulate online often come from other countries' labels, so they are the wrong guide for a UK KwikPen. Your patient information leaflet and your pharmacy are the right sources.¹³

Our full guide to how long Mounjaro can stay out of the fridge goes deeper on warm-weather and travel scenarios.

02 · Your next step

What to do with the pen in front of you

Start by finding which state your pen is in. If it is unused, check the expiry date on the box and make sure it is sitting in the fridge, not against the back wall where it could freeze. If you have already injected from it, work out the date of that first dose and count forward to the 30-day limit.

A simple habit helps: write the first-use date on the box or the pen label the day you start. A pen holds four weekly doses, so if you inject on the same day each week the final dose falls comfortably inside the 30 days. The limit mostly matters if you pause treatment, miss doses, or carry on after a break.

If something looks wrong, such as cloudiness, particles, discolouration, or a pen that may have frozen, do not inject. Contact the pharmacy that supplied it first. If you are thinking about starting treatment, the Mounjaro pen starting dose costs £169.99 per month at the standard price, and all six doses are in stock. Our wider weight loss clinic page explains how a free consultation works.

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

03 · Unopened pen storage

Storing an unopened Mounjaro pen

Unopened Mounjaro pens belong in the fridge at 2–8°C and keep until the expiry date printed on the box.¹¹³ That is the whole rule, and it is the same whether you ordered a single starter pen or several in advance.

Keep each pen in its original carton. The carton protects it from light and carries the batch number and expiry date you may need if you ever have to contact the pharmacy. Put it on a shelf in the main body of the fridge rather than in the door, where temperature swings are largest, and away from the freezer compartment or cooling element at the back.

Keep the pen cap on until you are ready to inject, as the cap protects the pen from light.¹ Treat the fridge as a place for medicine, not a shared drawer: keep pens away from anything that could crush or knock the carton, and out of reach of children.

People often ask whether a pen can be stockpiled. The expiry date on the box is the answer: an unopened pen kept correctly is good until then.

04 · In-use pen: 30 days

Your pen after the first injection

Once you have used a pen, the clock is 30 days (not above 30°C). 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, which is useful for short trips, and must then be thrown away.¹¹³

Two things follow from that. First, you do not have to keep an in-use pen out of the fridge; the allowance gives you flexibility rather than an obligation. Many people simply keep the pen in the fridge between doses and take it out only when injecting. Second, the 30 days (not above 30°C) run from the first use, not from the day it arrived or the day you took it out of the fridge. Going back into the fridge does not restart the count.

Because each pen contains four weekly doses, a pen used on schedule finishes inside the window.

For the opposite question, see how long Mounjaro can stay unrefrigerated.

05 · Why discard at 30 days

Why a pen is discarded after 30 days (not above 30°C)

A pen is discarded after 30 days because that is the window the manufacturer tested and licensed for an in-use pen. Beyond it, sterility and potency are no longer assured.¹

It helps to think about what an in-use pen goes through. A needle is attached for each injection, the pen is handled, carried and sometimes left in a bag or on a worktop. Each of those events is a small opportunity for contamination or temperature exposure. The licensed window exists so that those small risks stay inside what was tested.

You may see people online say they have kept using a pen beyond the limit and felt no difference. A pen can look perfectly normal and still be outside the tested window, and you cannot see or feel whether the medicine has weakened. The label is the only reliable guide, and following it costs you very little because a pen used weekly is already empty by then.

Does Mounjaro lose potency? Within the labelled storage conditions and dates, the medicine is expected to do what it is designed to do.

06 · Warning signs and freezing

How to tell if a Mounjaro pen has gone bad

A usable pen contains a clear, colourless solution, and you should 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.¹¹³

Run through a quick check each time you take a pen out:

• Is the expiry date on the box still in the future?
• If the pen is in use, are you still inside the 30-day limit from first use?
• Is the solution clear and colourless when you look through the window?
• Is there any cloudiness, colour change or visible particle?
• Could the pen have been near the freezer element or left in a cold hold or boot overnight?

If the solution is not clear and colourless, if there is any cloudiness, colour change or particle, if the pen could have frozen, or if you are unsure about the date checks, do not inject. Freezing is the quiet danger. A pen that has frozen may look normal once it thaws, yet it should never be used. Never freeze Mounjaro, and never use a pen that has been frozen.¹

Appearance checks cannot tell you everything. A pen that looks fine but has exceeded the licensed in-use window, or whose storage history you cannot account for, should still be discarded. When in doubt, the safe answer costs a conversation with the pharmacy; the unsafe answer could mean injecting a medicine whose strength you cannot vouch for.

Side effects or a new symptom after an injection should be discussed with your prescriber, and you can report them through the Yellow Card scheme.¹⁹

07 · Travel and heat

Travelling and warm weather

You can fly with Mounjaro, and most holidays need no special arrangements because in-use pens tolerate up to 30 days not above 30°C.¹ 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.

For hot climates use an insulated pouch. Heat is as much of a concern as cold: a pen left on a car dashboard, in a beach bag in direct sun, or in a parked vehicle on a warm day can easily exceed the labelled limit. Keep the cap on to protect it from light, and keep the pen with you rather than in a vehicle.

Unopened pens should be kept in the fridge and keep until the expiry date printed on the box. 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; figures circulating online often come from other countries' labels.¹

Before you fly, check the destination's rules for travelling with prescription injectables. Pack your needles and sharps disposal plan too, as many hotels have no way to take used needles. Our guide to how long Mounjaro can stay in its delivery box covers what to do when a parcel arrives and the fridge is not immediately to hand.

08 · Delivery and cold chain

Delivery, cold chain and what to do on arrival

Pens ordered from us travel in temperature-controlled, discreet packaging with free next-day tracked delivery, and same-day dispatch applies when you order by 3pm. Our Mounjaro comes through official LillyDirect supply, sourced directly from Eli Lilly's UK distribution, and every pen is a genuine KwikPen.

When the parcel arrives, open it promptly and move unopened pens into the fridge. Check that the box shows a batch number and an expiry date. If the packaging looks damaged, the pen seems to have been exposed to unusual conditions, or anything about the delivery seems wrong, contact the pharmacy before injecting. You can also check any pharmacy on the GPhC register; ours is registration 9012878.

Needles, a sharps bin and injection guidance are included with every order, so you have what you need to start. If you have questions on storage, our support team is available Monday–Friday 9am–5pm by email at support@everydaymeds.co.uk or by phone on 0333 207 0413.

Be cautious of any seller offering to supply Mounjaro without a consultation or prescription. A pen with no traceable supply route has no storage history you can trust, and counterfeit medicine alerts are published by the MHRA.⁷