Do You Have to Refrigerate Mounjaro? (October 2026)

01 · The short answer

Do you have to refrigerate Mounjaro?

Yes, unused Mounjaro pens should be kept in the fridge at 2–8°C until you are ready to start them. Keep each pen in its original carton so it is protected from light.¹ Stored this way, an unopened pen keeps until the printed expiry date.¹³

Once you have used the pen for the first time, the rule relaxes. UK KwikPens are licensed for up to 30 days (not above 30°C) out of the fridge once in use, so you do not have to refrigerate a pen you are actively injecting from.¹ Many people still keep it in the fridge between doses, which is fine.

We cover this in more detail in our guide on refrigerating Mounjaro after opening.

02 · What to do next

What should you do with a pen right now?

If your pen has not been started, put it in the fridge in its carton. If it is in use, note the date of the first injection so you know when the 30 days (not above 30°C) are up, and discard the pen after that even if medicine remains.

If your pen has been left out or got warm, do not rely on guesswork. Our guides on forgetting to refrigerate Mounjaro and what happens if it is not refrigerated go through the common situations.

If you are still deciding on treatment, the Mounjaro pen page has current doses and prices, and our weight loss clinic explains how a prescriber review works.

03 · Unopened pens

How to store unopened Mounjaro pens

Unopened pens go in the fridge at 2–8°C, in the original carton, until first use. The carton protects the pen from light, which is why it should stay in the box rather than loose in a fridge door.¹

Stored correctly, the pen keeps until the printed expiry date. That date is on the carton and the pen label. Never use a pen past it.¹³

Practical tips that follow from this:

• Put the carton on a main shelf, away from the back wall and the freezer compartment. Never freeze pens, and do not use a pen that has been frozen.
• Keep pens out of reach of children.
• If you hold several pens, keep them all in the fridge and bring out only the one you are starting.

If a pen is unopened but has been out of the fridge, check with the pharmacy before using it. Do not rely on a remembered day limit, because figures circulating online often come from other countries' labels.¹³ Our page on putting Mounjaro back in the fridge after room temperature covers that scenario.

04 · Pens in use

Storing a Mounjaro pen once you have started it

Once you have taken the first dose, a pen can be kept in the fridge or out of it, for up to 30 days (not above 30°C) in use.¹ The Mounjaro KwikPen is a multi-dose pen, so one pen covers several weekly injections.¹³

The 30 days (not above 30°C) run from the first use, not from when you took it out of the fridge. Write the first-use date on the carton or set a phone reminder. Throw the pen away after 30 days, or sooner if it has been above 30°C, even if some medicine seems left.

Should you let it warm up before injecting? The product information for the pen gives the injection instructions, so follow the pen's own instructions for preparing and giving the dose.¹³ Letting the pen warm briefly out of the fridge reduces stinging.

05 · Warm or left out

What happens if Mounjaro gets warm or is not refrigerated?

If an unused pen is stored outside its labelled conditions, the manufacturer's testing no longer covers it, so sterility and potency are no longer assured.¹ That is why the label conditions matter, rather than because a warm pen is instantly dangerous.

What to do depends on the situation:

• Pen in use, kept at normal room temperature: this is allowed for up to 30 days after first use, as long as it is not above 30°C.
• Unopened pen left out briefly: read the patient leaflet, then contact the pharmacy that dispensed it before injecting.¹³
• Pen that has been above 30°C or frozen: do not use it. Contact your prescriber or pharmacy for advice and a replacement decision.
• Pen that is cloudy or discoloured, or has particles in it: do not use it.

If a pen did not work as expected or you think it was stored badly, tell your prescriber. You can also report suspected problems through the MHRA Yellow Card scheme.¹⁹ Our page on what happens if you don't refrigerate Mounjaro has more detail.

06 · Deliveries and travel

Deliveries, travel and holidays

Our Mounjaro orders ship by free next-day tracked delivery in temperature-controlled, discreet packaging, and Saturday delivery is available for £14.99. Pens are genuine KwikPens supplied through official LillyDirect supply from Eli Lilly's UK distribution. When your parcel arrives, take the pens out and put any pens you are not about to use into the fridge promptly. Do not leave the parcel on a doorstep or in a warm porch for long.

For travel, the same rules apply. Unused pens should go back to fridge conditions as soon as you reach your destination, and the pen in use can stay out within its in-use window.¹

• Carry pens in your hand luggage, not the hold, where temperatures are not controlled.
• Keep pens in their carton so the label and your dispensing details travel with them.
• Use a small insulated bag for longer journeys.
• Never leave pens in a parked car or on a beach.
• Check destination rules for travelling with prescription injectables, and carry your needles and a sharps container.

If your trip is long, plan how many pens you need with your prescriber at your monthly review. Do not take extra doses or change the schedule to fit a holiday.

07 · Missed or delayed doses

Can you skip Mounjaro for a couple of weeks?

Speak to your prescriber before skipping doses, because the right advice depends on your dose, how long you have been treated and how you are feeling.

It helps to know how the medicine behaves in the body. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system — there is no way to speed this up, and nothing needs doing while it clears.¹

If a gap was caused by a storage problem, such as a spoiled pen waiting for a replacement, tell your prescriber so they can plan your restart. Our guide to forgetting to refrigerate Mounjaro is a good starting point if that is your situation.

08 · Other common questions

Timing, food and how long Mounjaro takes to work

There is no best time of day: Mounjaro works the same morning or evening, with or without food. What matters is the same day each week. Consistency makes the routine easier to keep.

How long does it take to work? Tirzepatide activates two natural gut-hormone receptors, GIP and GLP-1, which help regulate appetite and slow how quickly the stomach empties. In practice, most people feel fuller sooner and less hungry between meals.¹ How quickly you notice that varies from person to person.

What should you avoid, and can you eat bananas? No food is banned on Mounjaro, including bananas. Many people feel worse after very fatty, fried or very sugary food, and large portions sit heavily because the stomach empties more slowly, so smaller, slower meals work better. Treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them. Ask your prescriber or a dietitian for personal advice, especially if you take other medicines. If you notice a new symptom, tell your prescriber and report it through the Yellow Card scheme.¹⁹ 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.

09 · Peptides and storage

Why storage matters for a peptide-type medicine

Mounjaro pens should be kept in the fridge, and a pen that has been above 30°C or frozen must not be used. That is the practical reason for the fridge rule, and it is also why you should buy only from a registered pharmacy. Our page on whether Mounjaro has peptides explains what the medicine is made of.

Beware of anyone offering to supply tirzepatide without a consultation or prescription. You cannot trust the storage history of a pen from an unregulated seller, and counterfeit medicines are the subject of MHRA alerts.⁷ We are a GPhC-registered pharmacy (9012878) and supply genuine pens only. Prescriptions follow a free online consultation reviewed by a GPhC-registered prescriber.

Mounjaro is a prescription-only medicine used alongside a reduced-calorie diet and increased physical activity. Individual results vary, and this page is information, not a substitute for medical advice. If you want a quick reference for a similar question, see our page on whether you need to refrigerate Mounjaro.