The Mounjaro storage fridge rules come down to two stages. Keep unused KwikPens in the fridge at 2°C to 8°C, never let them freeze, and don't use any pen that has been frozen. Once you've injected from a pen, it can also be kept out of the fridge at up to 30°C, but either way it must be thrown away 30 days after that first use, even if medicine is left.
This guide follows the UK patient leaflet for the Mounjaro KwikPen (last revised August 2026, current as of September 2026) and the Instructions for Use. Mounjaro (tirzepatide) is a prescription-only medicine, and a prescriber decides whether it's suitable for you. This article is information only, not medical advice: your own leaflet, pharmacist and prescriber come first.
What are the Mounjaro storage fridge rules?
Before first use: fridge, 2°C to 8°C, never frozen
- Store unused pens in a refrigerator at 2°C to 8°C.
- Do not freeze them. If a pen has been frozen, don't use it, even once it has thawed.
- A pen kept in the fridge can be used up to the expiry date on the label and carton, which means the last day of that month.
After first use: up to 30°C for up to 30 days
Once you've given the first dose, the leaflet allows the pen to be stored out of the fridge at no more than 30°C for up to 30 days, after which it must be thrown away. The Instructions for Use add: keep it away from heat, keep pens and needles out of the sight and reach of children, and dispose of the pen after four weekly doses if that comes sooner.
Where in the fridge should Mounjaro go?
An ordinary kitchen fridge is fine; the aim is steady cool with no risk of freezing. A patient guide from Cambridge University Hospitals NHS Foundation Trust suggests keeping tirzepatide away from the cooling element, ideally towards the front of the fridge or in the door. In practice:
- Keep pens in their carton on a shelf or in the door, not pressed against the back wall.
- Keep them away from any ice box or freezer compartment.
- If you're unsure your fridge holds 2°C to 8°C, a simple fridge thermometer settles it.
How long can Mounjaro stay out of the fridge?
A pen you've started can stay out for up to 30 days at no more than 30°C, counted from your first injection with it. An NHS hospital guide confirms you can keep it in the fridge between doses; the 30-day limit from first use applies either way.
Each KwikPen holds four doses and Mounjaro is injected once a week, so a pen used on schedule gives its fourth dose three weeks after its first. The limit matters when a pen sits part-used for longer, such as after missed doses or a break in treatment, so write the date of first use on the carton. After the fourth dose, throw the pen away rather than trying to use what's left.
What about an unused pen that was left out?
The 30-day allowance applies only after first use: neither the leaflet nor the Instructions for Use gives a time allowance for an unused pen kept out of the fridge. If a new pen has been left out, or a delivery has sat somewhere warm, ask your pharmacist before using it.
What if a pen got frozen, too hot or looks wrong?
- Frozen: don't use it, even if it has thawed and looks normal.
- Above 30°C: the label only covers storage up to 30°C. If a pen has been somewhere hotter, such as a sunny windowsill or a parked car on a warm day, check with your pharmacist first.
- Damaged, cloudy, discoloured or with particles: don't use it. The medicine should be clear and colourless to slightly yellow.
If discarding a pen leaves you without a dose, contact the pharmacy or prescriber who supplies you. The leaflet's missed-dose rule: if it has been 4 days or less since the dose was due, inject as soon as you can; if it has been more than 4 days, skip it and take the next dose on your usual day. Never take a double dose, and keep at least 3 days between doses. Our dosage page explains the weekly schedule.
Only use pens prescribed for you and supplied by a registered pharmacy (GPhC in Great Britain, PSNI in Northern Ireland) or your NHS service. The MHRA warns against unregulated sellers such as beauty salons or social media: their pens, and so-called “compounded” versions, carry no assurance about what is in them or how they were kept. If you notice side effects, tell your prescriber or pharmacist; you can also report them through the MHRA Yellow Card scheme. Our side effects page covers what to expect.
Why do some websites say 21 days?
The 21-day figure belongs to single-dose pens and vials: the US prescribing information (revised August 2026) and the EU product information let those be kept unrefrigerated for up to 21 days in total. The US label also has its own KwikPen wording, including a 30-day room-temperature allowance for unopened pens that the UK leaflet doesn't give. As of September 2026, the only Mounjaro products listed on the emc are KwikPens, so go by the UK patient leaflet on the emc and the one in your own box.
How should I store Mounjaro when travelling?
- The pen you're using can travel at up to 30°C within its 30 days.
- Spare unused pens still need 2°C to 8°C, on the way and at the other end.
- Hot places: if it will be above 30°C, the in-use pen needs keeping cooler too. In a cool bag, wrap pens so they don't touch the ice pack, because a frozen pen can't be used.
When you fly, keep pens in your hand luggage: Cambridge University Hospitals' guide warns that the temperature in an aircraft cargo hold can drop below freezing. The National Travel Health Network and Centre (NaTHNaC) also advises contacting the airline in advance about injectable medicines, carrying a letter from your prescriber, and checking your destination's rules with its embassy or high commission.
Needles, caps and used pens: what else counts as storage?
- After each injection, unscrew the needle and put it straight into a sharps container. Don't store the pen with a needle attached: it can leak, block the needle and let air into the pen.
- Put the pen cap back on, and don't store the pen without it.
- Don't put loose needles in household waste, and don't recycle a used sharps container.
The leaflet also says not to throw medicines away via wastewater or household waste, so ask your pharmacist how to dispose of used pens and full sharps bins where you live; some councils collect them. For the full routine, see our how-to-inject guide, the first-injection walkthrough and our guide to injection sites and rotation.
Frequently asked questions
Does Mounjaro have to be kept in the fridge?
Unused pens, yes: at 2°C to 8°C, and never frozen. After first use, a pen can be kept out of the fridge at up to 30°C for up to 30 days, then thrown away.
Can I put an in-use Mounjaro pen back in the fridge?
Yes. Moving an in-use pen between the fridge and room temperature during its 30 days is fine. Either way, throw it away 30 days after first use or after the fourth dose, whichever comes first, and always take the needle off before storing it.
How long can an unused Mounjaro pen be out of the fridge?
The UK leaflet and Instructions for Use give no time allowance for unused pens; they belong in the fridge until you start them. If one has been left out, ask your pharmacist before using it.
Can I use a Mounjaro pen that has been frozen?
No, even if it looks normal after thawing. The leaflet says a pen that has been frozen should not be used. Dispose of it safely and ask your pharmacy about a replacement.
Can Mounjaro go in checked luggage on a plane?
It's best not to: an NHS hospital guide warns the cargo hold can drop below freezing, and a frozen pen can't be used. Keep pens in your hand luggage and contact the airline in advance. Our FAQ page answers more everyday questions.
Sources
- electronic medicines compendium (emc). Mounjaro KwikPen — Summary of Product Characteristics. medicines.org.uk
- electronic medicines compendium (emc). Mounjaro KwikPen — Patient Information Leaflet. medicines.org.uk
- Lilly Medical (UK). How should the Mounjaro (tirzepatide) KwikPen be stored? medical.lilly.com