What's the Shelf Life of Mounjaro? (October 2026)

01 · The short answer

How long does Mounjaro last?

Mounjaro lasts for the printed expiry date if the pen is sealed and kept in the fridge, and for up to 30 days (not above 30°C) once you start using it.¹ Those are the two numbers that matter.

The expiry date is printed on every carton and pen label. It applies only while the pen is stored as the leaflet describes, which means in the fridge until first use.¹³ The 30-day window starts when you first use the pen, not when it arrives at your door and not when you take it out of the fridge for the first time to warm up.

If you want the same topic split into narrower questions, we have separate pages on the shelf life of unopened pens and on how long a pen lasts after opening.

02 · Your decision

What should you do with your pen today?

Check three things: the expiry date on the carton, the date you first used the pen, and how the pen looks. If the date is still ahead, you are inside the in-use window, and the pen looks as it did when you opened it, you can carry on following your prescriber's schedule.

If you cannot remember when you started a pen, write the date on the carton from now on. Many people stick a label on the carton at the first injection. It is a small habit that removes any guesswork later, especially when you move between doses and have more than one pen in the house.

If you are unsure, contact the pharmacy that supplied it. Our support team is available Monday–Friday 9am–5pm. You can order from the Mounjaro pen page, where each strength is shown at £169.99 for 2.5mg up to £329.99 for 15mg; new customers save £40 on their first order with code FIRST40. Prices checked 11 October 2026.

03 · Unopened pen storage

How should you store an unopened Mounjaro pen?

Store unopened pens in the fridge at 2–8°C until you are ready to use them, and they keep until the printed expiry date.¹ It means the carton goes on a fridge shelf, not in a cupboard, a car or a bag, as soon as it arrives.

Keep the pen in its original carton. The carton carries the batch number and expiry date, and the patient information leaflet is inside it.¹³ Throwing the carton away makes it much harder to check what you have if a question comes up later.

Keep the carton in the fridge and keep the pen cap on to protect it from light. If you are unsure about freezing, light or what to do if an unopened pen has been out of the fridge, the leaflet is the place to look, and your pharmacy can advise on a specific case rather than guessing.

If you receive several pens together, for example while you are stepping up through the strengths, only the pen you are about to use needs to come out. The rest stay chilled and sealed. Our unopened shelf life guide goes into more detail on this.

04 · Pen in use: 30 days

Why does a pen only last 30 days (not above 30°C) once you start it?

A UK KwikPen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away.¹ Beyond that window, sterility and potency are no longer assured. The pen may look perfectly normal and still fall outside what has been tested.

The pen is a multi-dose device designed to cover your weekly injections across a four-week period. At the licensed once-weekly schedule, the contents are intended to be used within that in-use window. If your pen is not empty when the window closes, the remainder is not for use.

During those 30 days the pen can be kept in the fridge or out of it at a temperature not above 30°C.¹³

Our page on shelf life after opening covers how to track the date. Wegovy has its own in-use rules, covered on our Wegovy shelf life once opened page, and they should not be assumed to match Mounjaro's.

05 · Does it go bad?

Does Mounjaro expire or go bad?

Yes. Mounjaro has a printed expiry date, and a pen in use must be discarded after 30 days (not above 30°C).¹ Beyond those limits the medicine is outside the tested window, so you cannot rely on its strength or sterility.

Signs a pen may have been damaged are worth checking before every injection. Look at the liquid, the pen body and the label. Anything that looks different from how it looked when new is a reason to stop and call your pharmacy. Do not use a pen that has been frozen, looks cloudy or discoloured, has particles in it or has been above 30°C.

Do not rely on appearance alone, though. A pen can be past its in-use window and still look clear. The date, not the look, is the main test. Equally, a pen that is within its dates but has been exposed to conditions the leaflet warns about should be checked with the pharmacy before use.

If you notice an unexpected effect after an injection, speak to your prescriber, and you can report it through the Yellow Card scheme.¹⁹ Our related page can Mounjaro go bad expands on this.

06 · Leftover Mounjaro

Can you use leftover Mounjaro?

No, not once the pen has passed 30 days in use (not above 30°C) or its printed expiry date. Use the pen as designed, then dispose of it.

It is common to see liquid left in a pen at the end of the month and wonder if it is wasteful to throw it away. The pen is designed and licensed as a whole device for a set period. If you think a pen has the wrong amount in it, speak to your pharmacy or prescriber rather than improvising.

Do not put used pens in household waste. Use the sharps bin supplied with your order, and follow local guidance when it is full. Our service includes needles, a sharps bin and injection guidance with every order.

Pens that are in date but that you no longer need, for example because your dose changed, should not be passed to anyone else. Mounjaro is a prescription-only medicine, prescribed for one person after a consultation.¹

07 · Travel and heat

How do you keep pens safe when travelling?

A pen already in use can be kept out of the fridge at a temperature not above 30°C for up to 30 days, but unopened pens should stay in the fridge.¹ That distinction decides almost every travel question.

Carry pens in hand luggage, never the hold, which can fall below freezing, ideally in a cool bag with your prescription label or a copy of your prescription. A small insulated pouch is a low-cost accessory and is far safer than hoping for the best. For specifics on how long an unopened pen can be out of the fridge, the leaflet and your pharmacy are the right source, not a rule of thumb from a forum.¹³

Do not leave pens in a parked car, near a window in the sun, or beside a heater. On arrival at your destination, put the sealed pens in the room's fridge as soon as you can.

Carry your pharmacy label or prescription details when you travel with injectable medicines, as airport staff may ask what the pen is.

Deliveries are also temperature-controlled. We send free next-day tracked delivery in discreet, temperature-controlled packaging, with same-day dispatch when ordered by 3pm. Open your parcel promptly and put sealed pens in the fridge.

08 · Shelf life and body clearance

Is pen shelf life the same as how long Mounjaro stays in your body?

No. Pen shelf life is about the product in the device, while clearance is about the medicine in your body, and they are different questions. The same figure should not be applied to both.

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 In other words, four to five weeks after your last injection the drug is largely gone from the body, and that is unrelated to how long a pen lasts.

This matters for a practical reason. If you stop treatment, an unused sealed pen is not a safe-keeping arrangement. It is not a stockpile to use whenever you like. Talk to your prescriber before restarting, as dose decisions depend on your situation, and a pen already past its in-use window is never an option.

Our GLP-1 shelf life overview compares storage questions across this medicine class.

09 · Safe supply

Why does where you buy matter for shelf life?

A genuine pen from a regulated pharmacy has a traceable batch and expiry date, while pens from unregulated sellers may not, and storage history is unknown.⁷ Shelf life only means something if the pen has been kept properly from the manufacturer onwards.

The MHRA has issued counterfeit medicine alerts about GLP-1 products, and warns against sellers who offer to supply without a consultation or prescription.⁷ Check the pharmacy in the GPhC register. EverydayMeds is registered as GPhC 9012878.

We supply Mounjaro through official LillyDirect supply, sourced directly from Eli Lilly's UK distribution, as genuine KwikPens. Treatment is reviewed by a GPhC-registered prescriber after a free online consultation. If your consultation is declined, you are refunded automatically in full.

If you are a new customer, you save £40 on your first order with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25). Our weight loss clinic explains the full journey.

10 · Tracking dates

How can you keep track of dates?

Write the first-use date on the carton and set a phone reminder for the end of the in-use window.

A few habits help in practice:

• Check the expiry date as soon as the parcel arrives, before it goes in the fridge.
• Label the pen at its first injection, not later.
• Keep sealed pens at the front of the fridge shelf so you see them.
• Use the oldest pen first when you hold more than one pen of the same strength.
• Keep the leaflet with the carton for quick reference.

Our free GLPTrackr companion app (iOS and Android) can help you track your injections and your treatment journey. Ongoing monthly reviews with the prescribing team also give you a regular point to ask anything about storage.

If treatment is going well and you are working through the strengths, remember that each dose has its own pen, and each pen has its own clock. Starting a new strength means starting a new date. Mounjaro comes in six strengths, from 2.5mg to 15mg, and each pen is separate.¹ A related page, does Mounjaro have a shelf life, covers the basics, and fridge storage goes deeper on refrigerators.