How Long Can You Keep Mounjaro in the Fridge Unopened? (October 2026)

01 · The core answer

The short answer for an unopened pen

An unopened Mounjaro pen stays in the fridge until the expiry date on the box. There is no separate shorter countdown for a sealed pen that stays properly refrigerated.¹³ Keep it at 2–8°C, in its carton, and never let it freeze.¹

02 · Your next step

What to do if your situation is not simple

If your pen stayed in the fridge and is in date, there is nothing more to do. If it was left on a counter, in a hot car or in a delivery box for longer than expected, do not guess. Contact the pharmacy that dispensed it and tell them how long and how warm it was.¹³

Day limits quoted online often come from other countries' labels, so they may not match the UK product.¹ If you are still deciding on treatment, see the Mounjaro pen prices and consultation page; a first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99).

Related guides: How long can you keep a mounjaro pen unopened and Is it better to keep mounjaro in the fridge and How long does mounjaro last in the fridge unopened.

03 · Fridge storage rules

Storing sealed pens correctly

Keep Mounjaro pens in a fridge at 2–8°C and never freeze them.¹ Keep the pen cap on to protect it from light, and leave pens in their carton.¹³

A pen that has been frozen must not be used, even if it has thawed.¹

04 · The 30 day rule

Why the 30 days limit exists

Once a pen is in use, it can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹ A pen holds four weekly doses, so a pen used weekly fits within this window.

If you want to know about pens outside the fridge, see how long Mounjaro can stay out of the fridge.

05 · Signs a pen is unfit

How to tell if a pen is unusable

The solution inside a genuine pen is 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 in use for more than 30 days, or above 30°C.¹³

Appearance is not a full test. A pen that looks normal can still be outside its storage limits, so history matters as much as looks. If supply or packaging ever seems wrong, check the pharmacy on the GPhC register and contact them before injecting.

06 · Travel and deliveries

Travel, deliveries and cool bags

You can fly with Mounjaro. Carry pens in hand luggage, because hold luggage can fall below freezing, ideally in a cool bag with the prescription label or a copy of your prescription.¹³ For hot climates use an insulated pouch.

Unopened pens travel the same way as the fridge rule: they should be kept in the fridge and keep until the expiry date on the box.¹ Our orders arrive by free next-day tracked delivery in temperature-controlled packaging; put new pens in the fridge as soon as they arrive.

07 · Expired or leftover pens

Expired pens and leftovers

Do not use a pen past its expiry date. Its sterility and potency are no longer assured, and there is no safe way to test it at home. Ask your pharmacist how to dispose of it.

Do not combine leftovers from different pens. If you notice any unexpected symptom after using a pen, speak to your prescriber and report it through the Yellow Card scheme.¹⁹