Should I Keep Mounjaro in the Fridge After Opening? (October 2026)

01 · The short answer

Should you keep an opened Mounjaro pen in the fridge?

You can keep an opened Mounjaro pen in the fridge, and for many people it is the simplest habit. The UK guidance is that pens are kept in a fridge at 2–8°C and never frozen.¹ Once a pen is in use, the licence adds a flexibility: it can be kept out of the fridge for a limited time.

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 — useful for short trips — and must then be thrown away.¹ So the fridge is optional after opening, but the 30-day in-use limit is not.

That limit rarely causes trouble in practice. Each KwikPen contains four weekly doses, so a pen used once a week is finished well inside its in-use window.¹ The risk comes when someone holds a pen back, for example after pausing treatment, and keeps using it for longer than it should be used.

02 · Your next step

What should you actually do with your pen?

Pick one routine and stick to it. If you have space, put the opened pen back in the fridge with its cap on after every injection. If your fridge is crowded or you travel often, keeping the in-use pen somewhere cool and dark is within the licence, provided you count the days from first use.

Do not rely on memory for the 30-day limit. Note the first-use date on the box or in a reminder, or use the free GLPTrackr companion app to log your injections. If you are still comparing storage questions, our guides on keeping Mounjaro cold after first use and whether you have to refrigerate after opening cover the same ground from slightly different angles.

03 · In-use storage rules

How to store a Mounjaro pen once it is in use

Once a pen is in use, protect it from freezing, heat and light, and throw it away 30 days after first use (kept not above 30°C). The product information tells you to keep pens in a fridge at 2–8°C and never freeze them.¹ It also tells you to keep the pen cap on to protect it from light, and never to use a pen that has been frozen.¹³

Each of those points has a practical meaning at home.

• Fridge position: put the pen on a shelf rather than against the back wall, where items can freeze. A frozen pen cannot be used, so this is the mistake that costs people a pen.
• Cap on: the cap is there to protect the medicine from light, so replace it after each injection.
• Out of the fridge: a pen that lives on a shelf or in a bag should be somewhere cool, away from windows, radiators, cars and direct sun.
• Day count: the 30 days start when the pen is first used, not when it was delivered.

Needle handling is covered by the instructions that come with your pen. Needles, a sharps bin and injection guidance are included with every EverydayMeds order, so follow the pen's own instructions for fitting and disposing of needles rather than improvising.

If you want a deeper look at how long a pen stays usable once opened, see our guide to Mounjaro expiry after opening.

04 · Is the fridge better?

Is the fridge better than room temperature?

The fridge is the default storage condition in the product information, while room temperature is a permitted allowance for pens already in use.¹ That means neither choice is wrong for an opened pen, but the fridge asks less of you.

Reasons people prefer the fridge after opening include a hot kitchen or a warm home in summer, a household where the pen could be mislaid, and simply having one place for everything. Reasons people prefer room temperature include the injection feeling more comfortable when the pen is not straight from the cold, and having the pen with them at work or travelling.

What the product information does say is that the pen must stay within its limits. For a longer discussion of the trade-offs, our pages on whether it is better to keep Mounjaro in the fridge and how long you can keep it in the fridge go further.

One caution: do not push a pen to the back of a very cold fridge to "be safe". A pen that has frozen must not be used.

05 · Travelling with your pen

Travelling with an opened Mounjaro pen

You can fly with Mounjaro, and most trips need no special equipment. Carry pens in hand luggage, because hold luggage can fall below freezing.¹ Ideally, pack them in a cool bag with the prescription label or a copy of your prescription.

In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements. For hot climates, use an insulated pouch.¹ Check destination rules for travelling with prescription injectables before you fly.

A sensible packing routine looks like this:

• Keep the pen in its box or case, with the cap on, in your hand luggage.
• Pack the prescription label or a copy of your prescription alongside it.
• Use an insulated pouch in hot destinations and keep the pen out of parked cars and direct sun.
• Do not put the pen against an ice pack in a way that could freeze it. A cool bag is for keeping the pen cool, not frozen.
• If your injection day falls during the trip, plan where and when you will inject before you leave.

If you are travelling with a pen you have not yet opened, remember it belongs in the fridge until first use. An unopened pen that has been out of the fridge should be checked with the pharmacy before use rather than judged by a day limit you read online, since figures circulating online often come from other countries' labels.¹

06 · Spotting a bad pen

How to tell if a Mounjaro pen has gone bad

A pen is not safe to use if it has been frozen, has been above 30°C, looks cloudy or discoloured, has particles in it, is past its expiry, or has been out of the fridge for more than 30 days in use.¹ The solution inside a genuine pen is clear and colourless.

Run through this before every injection:

• Look at the solution: it should be clear and colourless, with no cloudiness, colour change or particles.
• Check the date: look at the printed expiry date on the box and pen.
• Count the in-use days: if the pen has been in use for longer than its limit, discard it even if medicine appears to remain.
• Think about freezing: if it could have touched the back of the fridge, an ice pack, or been in a cold hold, do not use it.

You cannot always tell by eye that heat or time has affected a medicine, which is why the day count and date matter as much as appearance. When in doubt, do not inject. Contact the pharmacy that supplied the pen and ask.

Supply matters too. A genuine UK pen comes from a registered pharmacy with a batch number and expiry date, and arrives cold-chain packaged.¹ If packaging or supply ever seems wrong, check the pharmacy on the GPhC register and contact the pharmacy before injecting. Offers to supply without a consultation or prescription are a red flag. Any side effect or suspected problem with a pen can be reported through the Yellow Card scheme.¹⁹

07 · Why storage matters

What happens if you do not store a pen properly?

A pen stored outside its limits is outside the conditions the manufacturer tested, so potency and sterility are no longer assured.

That is why the freezing rule is the strictest. The leaflet says never to use a pen that has been frozen.¹³ A pen out of the fridge for longer than the in-use allowance falls into the same category.

If you miss an injection, the rule is different from storage and worth knowing: 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

08 · Other GLP-1 pens

Do other GLP-1 medicines follow the same rules?

Do not assume so. Every medicine has its own leaflet, and the figures differ by product and by country.

If you use Wegovy or another injectable, read that product's patient leaflet for its own storage and in-use limits, and ask your pharmacist if anything is unclear. Do not carry a number from one medicine over to another. The same warning applies to storage tips found online: many come from other countries' labels, which is exactly the trap the UK product information flags.¹

For Mounjaro, the pattern is consistent across the pen's life: the fridge is the default, in-use pens have a limited out-of-fridge allowance, freezing is never acceptable, and cap on protects from light.

If you are weighing up treatments more broadly, our weight loss clinic page explains the options and how a prescriber reviews them.

09 · Storing after delivery

What to do when your pen arrives

When your pen arrives, check it and get it into the fridge straight away if you are not using it that day. Our orders are dispatched the same day when placed by 3pm, with free next-day tracked delivery in temperature-controlled, discreet packaging.

Then follow a simple sequence:

• Check the box shows a batch number and expiry date, and that the solution looks clear and colourless.
• Store the unopened pen in the fridge until you need it. It keeps until the printed expiry date.¹
• Record the first-use date, then store the opened pen in the fridge or in a cool place with the cap on.
• Discard the pen when its in-use period ends, or when it is empty.

Injection day itself does not affect storage. You can inject at any time of day, with or without food, and the same day each week is what matters.¹ If you need help with a pen that arrived warm or damaged, contact us Monday to Friday, 9am to 5pm, on 0333 207 0413 or at support@everydaymeds.co.uk. Faulty, damaged or wrong items should be reported within 3 days.

10 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹