How long can you keep Mounjaro in the fridge unopened?

Why the fridge temperature range matters more than the calendar date

The question most people are really asking is: "I have a pen sitting in my fridge, is it still good?" The answer turns on two things acting together: the printed expiry date and whether the pen has been stored correctly throughout its time in your fridge.

Mounjaro must be kept at 2°C to 8°C. That sounds precise because it is. A fridge door swings open, temperature spikes, and edges toward 10°C or higher during a long dinner party. The back of the fridge near the freezer plate can dip below 0°C. Neither is acceptable. The safest spot is a middle shelf, away from the walls and the door.

If you are unsure what temperature your fridge actually runs at (rather than what the dial claims) a cheap thermometer placed on the shelf for 24 hours will tell you. It is a five-minute check worth doing once. For more on what happens when a pen leaves the fridge temporarily, the guidance on how long an unopened pen can be out of the fridge covers that scenario in detail.

The NHS tirzepatide medicines page confirms that Mounjaro should be stored in a fridge and kept away from direct heat and light.

Reading the expiry date correctly, and what to do when timing is tight

The expiry date on a Mounjaro pen is expressed as month and year (for example, 04/2027). The pen is valid through the last day of that month. So a pen marked 04/2027 is fine on 30 April 2027 and should not be used from 1 May 2027 onwards.

Timing catches people out more than they expect. If your delivery arrives in late November and you are not due to inject until after Christmas, the pen may comfortably cover the gap. But if you are planning ahead and ordering for a holiday period, or you are waiting for payday before placing a repeat order, it is worth factoring the expiry date into when you reorder rather than assuming stock will always have months in hand. A quick check of the date when the pen arrives takes seconds and can prevent a wasted pen later.

If you need clarity on how storage time accumulates across multiple pens or across a dose change, the full detail on how long an unopened Mounjaro pen lasts in the fridge is worth reading alongside this page.

Questions about your specific supply or treatment timeline are exactly the kind of thing to raise with your prescriber; at nume, our clinical team is available for aftercare seven days a week.

Deciding what to do with a pen you're not sure about

This is the practical crux for most readers. You have a pen. Something has happened, it sat in a warm car, the fridge broke overnight, you noticed it might have been too close to the freezer plate. The decision is binary: safe to use, or not.

Do not use a pen if it has been frozen. Ice crystals can damage the protein structure of tirzepatide even if the pen looks normal once thawed. Do not use it if you notice any cloudiness, discolouration, or floating particles, the solution should be clear and colourless. Do not use it past its expiry date. If any of those apply, the right move is to speak to your prescriber before injecting.

For disposal, a used or expired pen counts as clinical waste and should go into a proper sharps container rather than a household bin. If you need one, a 1-litre sharps container is available through our pharmacy. On the broader question of what to do with pens at end of life, our page on recycling Mounjaro pens explains the options.

If you are starting treatment or thinking about how Mounjaro fits into a medically supervised weight-management plan, a prescriber can also talk through storage alongside everything else during the consultation process.

Storing multiple pens and planning ahead

Each Mounjaro KwikPen contains four weekly doses. If you are on a higher strength and building up a stock of pens, it is worth treating them the same way you would perishable food: first in, first out. Use the pen with the earliest expiry date first and keep newer stock behind it on the shelf.

It is also sensible to double-check that nothing in your fridge is sitting on top of a pen or pressing against it. Mechanical pressure will not damage the medicine itself, but a pen that rolls to the back and gets partially frozen is a different matter. Keep them upright or lying flat in a designated spot, away from anything that could block cold-air circulation.

If you have questions about maximum storage times across the range of Mounjaro strengths, or about how the injection process itself should go once you do open a pen, the Mounjaro injection guidance covers technique and rotation in one place. And if you are weighing up the cost of keeping a private prescription going, a clear look at Mounjaro pricing in the UK sets out what to expect.

Ready to get started or review your current plan? Start your free consultation and a GPhC-registered prescriber will review your case the same day.