Shelf Life of Mounjaro in the Fridge: UK Storage Guide (October 2026)

01 · The short answer

How long does Mounjaro last in the fridge?

An unopened Mounjaro KwikPen lasts in the fridge until the expiry date printed on its box. Keep it at 2–8°C and never freeze it.¹ There is no separate shelf life to calculate for an unopened pen: the printed date is the limit, provided it has been stored properly the whole time.

Once you start using a pen, a different clock applies. An in-use pen can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹¹³ That 30 days (not above 30°C) is the cap for the pen in use. We have a separate page on the wider Mounjaro shelf life question if you want the full overview.

The pen is a multi-dose pen, which is why the 30-day rule matters. If you are ever unsure whether a pen is still within its window, ask the prescribing team before you inject rather than guessing.

02 · What to do next

The decisions most people are actually facing

Most storage questions fall into three situations. First, a new pen has arrived and you want to know where to put it: place it in the fridge until you are ready to start, keeping the cap on. Second, you have started a pen and want to know how long it is good for: up to 30 days, then discard. Third, something has gone wrong, such as a pen left in a warm car, a pen that has frozen, or a pen of uncertain age.

For the third situation, the rules are firm. 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.¹³ For an unopened pen that has been out of the fridge, contact the pharmacy that supplied it and follow the patient information leaflet rather than relying on a figure you saw on a forum.

If you are comparing providers and want to see what a pen costs, the Mounjaro pen with prices and consultation page shows current dose prices, with the 2.5mg starter at £169.99 per month at the standard price. Our weight loss clinic page explains how treatment and follow-up work.

Related guide: Does mounjaro have a shelf life.

Related guide: Mounjaro shelf life unopened.

03 · Unopened pens

Unopened pens: fridge storage until the expiry date

An unopened Mounjaro pen should live in the fridge at 2–8°C until you start it, and it keeps until the expiry date printed on the box.¹¹³ That printed date is the only shelf-life figure that applies to a sealed pen stored correctly.

The honest answer is that the number is on your box. It differs from batch to batch, so a figure quoted on a website could be wrong for the pen in your hand. Always read the printed date, and check it again before you start a new pen if it has been stored for a while.

When your pen arrives, it comes in cold-chain packaging so it has been kept cool in transit. Take it out of the delivery packaging, check the box for the batch number and expiry date, and put it in the fridge. If you plan to start it within a short time, it is still best to keep it cold until then. Keep the cap on to protect the pen from light, as the storage guidance advises.¹

Where should it go in the fridge? The safest approach is a place where it will not freeze, because freezing damages the pen and a frozen pen must never be used. Avoid pushing it right against the back wall or next to the freezer compartment, and do not put it in a freezer drawer for convenience. A door shelf is often a reasonable choice in a household fridge, but the principle is simply cold, not frozen.

Keep pens in their carton so they are protected from light and easy to identify. If you hold more than a single pen, for instance when you step up to a higher strength, keep each strength separate and labelled so there is no confusion about which pen is which.

What if the fridge has a power cut or has been turned off by mistake? Do not assume the pen is fine or ruined. The patient information leaflet and the supplying pharmacy are the right places to turn.

Finally, store pens out of the reach of children, and keep unused pens separate from food that could leak or contaminate the carton.

04 · In-use 30-day rule

Pens in use: the 30-day limit

Once you start a Mounjaro pen, it can be kept for up to 30 days, either in the fridge or out of it not above 30°C, and then it should be discarded.¹¹³ This is the figure that matters for day-to-day use, and it is the one UK patients should follow.

The 30 days run from when you first use the pen, not from when it arrived. That distinction is the source of a lot of confusion. A pen sitting unopened in your fridge is on the printed-expiry clock. A pen you have injected from is on the 30-day clock. If you are keeping track, note the date of the first injection on the carton or in an app. Our free companion app, GLPTrackr, can help you track your journey on iOS and Android.

Does the 30-day limit depend on whether the pen is in the fridge? A pen in use can be kept in the fridge or at a temperature not above 30°C, for up to 30 days after first use. So putting it back in the fridge between doses does not extend the window, and leaving it on a shelf at ordinary room temperature does not shorten it, as long as it stays not above 30°C.

What happens on day 31? Discard the pen, even if there is medicine left in it. That can feel wasteful, particularly if you have had a missed dose or two, but the pen must be thrown away after 30 days.

People often ask about a pen that has been in the fridge for more than 30 days, or above 30°C after first use. The answer is the same: the pen should be discarded after 30 days (not above 30°C) in use, whether it has been stored cold or at room temperature. The cold does not turn the limit into something longer.¹³ Our guide to what the shelf life of Mounjaro means explains the two clocks side by side.

Is there a way to avoid waste? Tell your prescribing team if your timing changes, for example because you are pausing or changing dose. If a dose change is on the way, ask in advance how it affects the pen you are on. The team can adjust the plan with you at your monthly review.

In short: write the start date down, use the pen within 30 days, keep the cap on between doses, and bin it afterwards in a sharps bin. Needles, a sharps bin and injection guidance are included with every order from us.

05 · Out of the fridge

Out of the fridge: how long is too long?

An in-use pen tolerates up to 30 days not above 30°C, so a pen out of the fridge for ordinary daily use is within its licensed window.¹ An unopened pen is different: it should be kept in the fridge, and any time out of the fridge is a reason to check with the pharmacy.

For a pen already in use, the answer is the 30-day limit not above 30°C. For a pen that has not been started, keep it in the fridge until first use; it keeps until the printed expiry date.

You may see day figures online for how long tirzepatide can be left out. Many of them come from other countries' labels, and those labels can differ from the UK one. If you read a number on a forum or in an American article, treat it as not applying to your UK KwikPen. The patient information leaflet in your box, and the pharmacy that dispensed the pen, are the reliable sources.

Here is a sensible way to think about an unopened pen that spent time out of the fridge. Ask yourself how warm it got, for how long, and whether it froze. If the answer is a short spell at normal room temperature, contact the pharmacy, explain what happened, and let them advise. If the pen sat in a hot car, a sunny windowsill or near a heater, tell them that too, because heat is a different risk from a mild room temperature. Until you have an answer, hold off injecting from it.

The same logic applies to questions about other medicines, such as semaglutide pens or insulin. Each has its own label and its own storage rules, and they are not interchangeable with Mounjaro. If you use one of those, read its leaflet and ask its prescriber or pharmacist. For Wegovy, see our page on Wegovy shelf life once opened, and for the wider family of medicines, the GLP-1 shelf life overview.

One more practical point: if you inject from a pen kept at room temperature, it is sometimes more comfortable than a very cold pen straight from the fridge. That is a comfort point only. It does not alter the in-use limit, and you should still keep the pen not above 30°C with the cap on, away from direct light.

06 · Freezing and heat

Freezing and heat: when a pen must be thrown away

Never freeze Mounjaro, and never use a pen that has been frozen.¹ If a pen has frozen at any point, discard it, even if it looks normal after thawing. That is a firm rule in the UK storage information.

Freezing can happen more easily than people expect. A pen stored against the back of a fridge, next to the freezer compartment, or in a very cold part of the fridge can freeze. So can a pen in hold luggage on a flight, because hold luggage can fall below freezing. Pens left in a car overnight in winter are also at risk. If there is any chance that a pen has frozen, treat it as frozen and speak to the pharmacy.

Heat is the other side of the problem. The in-use allowance is for temperatures not above 30°C, so a pen that gets hotter than that, for instance in a car on a summer day, sits outside the label. For hot climates, an insulated pouch is the suggested approach for travel.¹³ If a pen has been exposed to heat above that limit, do not simply carry on using it. Contact the pharmacy and ask.

How would you know a pen has been damaged? You may not always be able to tell by looking. The solution in a genuine pen is clear and colourless, so cloudiness, discolouration or particles are warning signs, and any of them means the pen should not be used.¹³

A short checklist you can apply any time: has it frozen, has it been in the heat, is it cloudy, does it have particles, is it past its expiry, has it been in use for more than 30 days, or above 30°C? A yes to any of these means do not use it. If you are unsure, the answer is to ask rather than inject.

What about light? The cap protects the pen from light, so keep it on whenever you are not injecting. Leaving the pen uncapped on a sunny shelf is a poor habit even if it is not a dramatic risk on any single day. Treat the cap as part of the storage system, not an optional extra.

If you do discard a pen because of a storage problem, tell your prescriber. They can talk through the timing of your next dose and whether you need a replacement, so that your treatment is not disrupted more than necessary. If you notice anything unusual after using a pen, tell your prescriber, and you can report suspected side effects through the MHRA Yellow Card scheme.⁷

07 · Checking a pen

How to check a pen is genuine and still good

A genuine UK Mounjaro pen comes from a registered pharmacy with a batch number and expiry date, arrives cold-chain packaged, and contains a clear, colourless solution.¹³ Run through these checks before each new pen, not only the first.

Start with the supplier. A regulated pharmacy will appear on the GPhC register, and you can check ours (GPhC 9012878) on the GPhC register.¹² Our Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens. If supply or packaging ever seems wrong, check the pharmacy on the register and contact it before injecting.

Then check the box. There should be a batch number and an expiry date. If either is missing, smudged or looks altered, do not use the pen. Counterfeit medicines are a real concern for weight-loss injections, and the MHRA publishes counterfeit alerts and runs the Yellow Card scheme.⁷ Anyone offering to supply without a consultation or prescription should be treated with suspicion.

Next, look at the pen and the liquid. The solution should be clear and colourless. 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.¹³

Finally, review the history. Where has the pen been since it arrived? Did it go in the fridge promptly? Has it been in a bag, a car or a suitcase? A pen with a clean history, a legible date and a clear solution is ready to use. A pen with any doubt attached should be queried with the pharmacy first. Contacting us costs nothing: our support team is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, through account portal chat, or by phone on 0333 207 0413.

Keep the carton until the pen is finished. It carries the batch number and expiry date, which are useful if you ever need to report a problem or ask a question about that specific pen. Throw the pen away safely in a sharps bin when it is empty or reaches the end of its in-use window.

08 · Travelling

Travelling with Mounjaro pens

You can fly with Mounjaro, and most holidays need no special arrangements because an in-use pen tolerates up to 30 days not above 30°C.¹³ The main things to get right are where the pens travel, how they are kept cool, and the paperwork.

Carry pens in hand luggage, because hold luggage can fall below freezing. Ideally use a cool bag, and carry the prescription label or a copy of your prescription. Check the destination's rules for travelling with prescription injectables before you fly, as requirements differ between countries. Security staff are generally used to medical items, but having the label and documentation to hand makes things smoother.

For short trips, a pen you are already using can simply travel with you not above 30°C. For hot climates, use an insulated pouch so the pen does not climb above that limit in a hot vehicle, on a beach bag or in direct sunlight.

What about unopened spare pens? These should be kept in the fridge and they keep until the printed expiry date. If you are going away for long enough that you need an unopened pen with you, think about where it will be stored on arrival. Ask your accommodation whether a fridge is available, and bring the pen in a cool bag for the journey. If an unopened pen has been out of the fridge for any length of time, check with the pharmacy before using it rather than relying on a remembered day limit.¹³

Time zones and your weekly injection day can be awkward on long trips. Speak to your prescriber if you expect your injection day to fall during travel, and plan around it in advance. Do not change your dose or schedule without advice.

At the end of a trip, put any unopened pens back in the fridge straight away and note how long your in-use pen has been going so you stay inside the 30 days (not above 30°C).¹

Receiving a delivery while away is usually a poor idea. Our free next-day tracked delivery uses temperature-controlled packaging, but the best plan is to have it sent to an address where someone can receive it and get it into the fridge quickly.

09 · Myths and mix-ups

Myths, mix-ups and figures from other countries

Most confusing numbers about Mounjaro storage come from other countries' labels or from guesses, and the UK figures are simple: printed expiry date for unopened pens stored cold, and 30 days (not above 30°C) in use.¹ If a figure you have read does not match those, it probably relates to a different market or a different medicine.

One common mix-up is between the in-use limit and the date on the box. The expiry date is for unopened pens kept in the fridge. The 30-day limit is for the pen once you have started it. The earlier of the two applies: if the printed date falls before the end of your 30 days, do not use the pen past the printed date.

Another mix-up is the idea that the fridge pauses the in-use clock. It does not. The pen in use can be kept in the fridge or out of it not above 30°C, but the limit is 30 days either way. Likewise, you may hear that a pen can be used until it is empty regardless of age. The UK instruction is to discard it after 30 days even if medicine remains.

Questions about other injectables are similar, for example how long a pen of semaglutide or insulin can be left out. Check each product's patient information and ask the prescriber or pharmacist who looks after it.

Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. A new-customer discount applies to first orders and a reorder discount to every future order. The current values and codes are shown on our product page.

10 · Everyday habits

Everyday habits that protect your pens

A few simple habits keep every pen inside its label limits: put new pens in the fridge on arrival, note the first-use date, keep the cap on, and discard at 30 days (not above 30°C).¹ None of them take much effort once they are routine.

On delivery day, open the parcel promptly. Our deliveries use temperature-controlled, discreet packaging and arrive on a free next-day tracked service, with same-day dispatch when ordered by 3pm. Track your parcel, be home or arrange a safe place, and get the pens into the fridge soon after arrival. Do not leave a delivery sitting in a porch in hot or freezing weather.

At the point of starting a pen, write the date on the carton. If you use a tracking app, log the injection there too. Some people set a repeating reminder for the end of the in-use window, so the pen is replaced on time instead of lingering in a drawer.

Between doses, put the cap back on straight away and store the pen where it is easy to find but not exposed to heat. Whether you choose the fridge or a cool shelf at home, keep it not above 30°C. If you keep it in the fridge, make sure it is not touching the back wall or freezer compartment.

Plan around your own routine. If you are going to be away from home on your injection day, pack a pen in a cool bag. If you are changing dose, ask your prescriber how the change affects the pens you hold.

Review your supply at each monthly check-in. Ongoing monthly clinical reviews are included with our service, along with dose titration and follow-up assessments by the prescribing team. Repeat orders re-check suitability, and there is no auto-shipping, so you control the timing of what arrives. That helps you avoid stockpiling pens that may drift towards their expiry date.

If you ever stop treatment, remember that 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.¹ Leftover pens should be disposed of safely rather than kept past their storage limits. Ask the pharmacy about safe disposal if you are unsure.

Availability on the NHS is being phased in over several years, with the primary-care rollout beginning in June 2025 for the highest-need groups first.⁶