Storage and the cold chain

What the fridge is actually for

These medicines are peptides — chains of amino acids — and peptides are fussier than the small molecules most of us are used to swallowing. Warmth speeds up the chemistry that degrades them and encourages the individual molecules to clump together, a process called aggregation. Neither of those turns the liquid into poison. What they do is quietly reduce how much intact, active drug is in the syringe, and possibly increase the chance of an immune reaction to the aggregated material.

That is the honest frame for everything below. A broken cold chain is usually a potency question, not a toxicity question. It is also mostly invisible: degraded peptide looks exactly like fresh peptide. You cannot inspect your way to confidence, which is why the storage rules exist in the first place.

The universal number is two to eight degrees Celsius — the ordinary working range of a domestic fridge. Every GLP-1 product we know of specifies it for unopened storage. Where products differ enormously is the in-use period: how long a pen or vial you have started may be kept out of the fridge, at what maximum temperature, and whether the clock keeps running if you put it back in the cold. Those windows range from roughly three weeks to roughly six weeks depending on the product and the country's approved labelling, so we are not going to print a number here. Read your leaflet, and if it has gone missing, a pharmacist can tell you in under a minute.

Freezing is the one that ends it

If the medicine has frozen, it is finished. Every manufacturer says the same thing in the same flat language: do not use if it has been frozen, even if it has thawed and looks normal. Freezing physically disrupts the protein structure and no amount of gentle handling brings it back.

This matters because domestic fridges freeze things constantly by accident. The coldest spots are against the back wall, directly under the cold-air outlet, and in the bottom of the salad drawer of some models. Members have lost an entire month's supply to a fridge that was, on average, at four degrees but had a back shelf sitting below zero.

Two cheap defences. A small fridge thermometer, left where you actually keep the medicine rather than in the middle of the fridge, costs very little and settles the argument. And the middle shelf, towards the front, away from the back wall, is the most stable place in most domestic fridges — not the door, which swings through room temperature every time somebody wants milk. What goes in your fridge and what does not covers the geography in more detail.

Ice crystals visible in the liquid, or a pen that seems oddly cloudy after a cold snap, means stop and ring the pharmacy. Do not inject and hope.

Excursions: warm, brief, and what to do about them

An excursion is any period outside the labelled range. They happen to everybody eventually and the community's collective instinct — throw it away in a panic, or use it and say nothing — is wrong in both directions.

The useful reflex is to record it and then ask. Write down what happened, roughly how warm it got, and for how long. Then ring the pharmacy or the prescribing service with those three facts. Manufacturers hold stability data that is not printed on the leaflet, and pharmacists can often get a straight answer from a medical information line. Mira's experience from the clinical side is that this call is answered helpfully far more often than members expect, and that people who guess in silence are the ones who end up either wasting money or injecting something that has been in a car in August.

Some rules of thumb that are not a substitute for that call. A pen out of the fridge overnight in a cool British bedroom is a very different event from a pen in a glovebox in Queensland. Repeated warm excursions add up, even if each one is short. And unopened supply that has never been out of range is the stock you protect first — if something has to be risked, risk the pen you are already using.

Never put a warmed pen in the freezer to catch up. That converts a possible problem into a definite one.

Deliveries, doorsteps and heatwaves

If your medicine is posted to you, the cold chain includes a stranger in a van. Well-run pharmacy services ship in insulated packaging with coolant and aim for next-day delivery; the failure modes are a parcel left in a porch in a heatwave, a missed delivery that spends a weekend in a depot, or a neighbour who puts it somewhere sensible-looking and warm.

What members do, in rough order of how much difference it makes: arrange delivery to a day and address where somebody is genuinely present; never use a safe-place instruction for medicine; open the parcel the moment it arrives rather than that evening; and check whether the coolant is still cold and whether the packaging has obviously been in the sun.

If it arrives warm, do not put it in the fridge and carry on quietly. Photograph the packaging, note the time, and contact the pharmacy the same day — reputable services replace parcels that have failed in transit, and they cannot do that once you have used half of it. Noah lost a fortnight of treatment to a parcel that sat in a locked porch over a bank holiday, and the pharmacy replaced it without argument once he rang; he had assumed for two days that it was his own fault.

In a heatwave, think about the journey home from the pharmacy as well. Fifteen minutes on a hot bus is an excursion. A cheap insulated bag in the cupboard solves it permanently.

Power cuts, house moves and the fridge that dies

A closed fridge holds its temperature for several hours in a power cut — the enemy is opening it. If the power is out, leave the door shut, and if it is going to be a long outage, think about a cool box with ice packs rather than moving things around repeatedly.

A fridge that has failed silently is worse than one that has visibly died, which is the other argument for a thermometer. Members who work shifts or travel for work are the ones who most often come home to a warm fridge and no idea how long it has been that way.

For a house move, treat the medicine as hand luggage: an insulated bag with a cool pack that is not in direct contact with the pens, kept with you rather than in the van. The same applies to a hotel stay during a move; ask reception for a proper fridge rather than trusting a minibar, which is often a warm cabinet with a light in it.

Finally, the accounting nobody enjoys. If you have lost a supply, work out whether you have enough to reach your next prescription and, if not, start that conversation immediately rather than at the end. Gaps compound: a lost fortnight can become an unplanned restart, which has its own consequences described in what to do if you miss a dose and, if the gap runs longer, in shortages and substitutions.

If you have vials rather than pens

Everything above applies, and then some. Reconstituted material — powder that you have mixed with bacteriostatic water — has a shorter and much less well-defined life than a sealed manufactured pen, and the guidance you find online varies wildly because for compounded and research-use material there is often no manufacturer stability data at all.

What we will say plainly: an unlabelled vial in a fridge is a hazard to you and to anyone else in the house. Write on it, in permanent marker, what it is and the date you mixed it. Keep it upright, away from the door and the back wall, and keep the powder and the water in their original packaging until the day you use them.

We are not going to give you an expiry rule for reconstituted material, because we do not have one that is honestly supported. The bacteriostatic preservative in the water is there to inhibit bacterial growth after repeated needle entries; it does nothing about chemical degradation of the peptide, and those are separate clocks. Reconstitution, doing the maths together goes through the arithmetic and the honest limits, and sourcing outside a prescription is the guide to read if this is the route you are on.