Carrying Medication on the Mountain: Sub-Zero Storage and What to Keep on Your Body

Cold air destroys insulin, freezes auto-injectors, and renders inhalers useless. Here is what actually fails at altitude and how to stop it.

Sub-zero medication storage: the mountain rules are different

Frozen insulin is not the same as cold insulin. Once insulin crystallises, it cannot be thawed back to an effective formulation. Most high-altitude hikers, ski tourers, and expedition climbers know to keep insulin away from heat. Far fewer know that a night in a tent at -15°C will destroy a pen left in a pack.

This article is about the physical reality of carrying prescription medication in alpine and high-latitude environments: what freezes, what degrades, what stops working mechanically, and which medications must stay on your body rather than in your bag.

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Medication storage and management in extreme environments should be discussed with your prescribing clinician or a travel medicine specialist before you depart.

What actually freezes (and at what temperature)

Insulin freezes at approximately -2°C to -4°C depending on formulation. The World Health Organization cold-chain guidelines confirm that frozen insulin must be discarded, not used.^[5] That temperature is reached inside a pack resting against snow overnight, inside a cold tent at elevation, or strapped to the outside of a sled.

Epinephrine auto-injectors present a different failure mode. The adrenaline molecule itself degrades in heat, but the mechanical spring mechanism in EpiPen and Jext devices can freeze and fail to trigger below -20°C. A device that looks intact may not deploy.

Pressurised metered-dose inhalers (pMDIs) lose effective dose output in cold air. At -20°C, pMDI output can drop by 20 to 30 percent because the propellant pressure falls. Dry powder inhalers (DPIs) are less affected by cold but are highly sensitive to moisture, which is a separate alpine risk.^[1]

Biologics, including adalimumab, etanercept, and most GLP-1 receptor agonists, must stay between 2°C and 8°C.^[6] Freezing denatures the protein structure irreversibly. There is no visual change when a biologic freezes and thaws. You cannot tell by looking.

On your body, not in your bag

The core rule is straightforward: any medication that freezes below body temperature must be kept against your body, not stored in a bag or pocket exposed to ambient air. Your torso runs at roughly 37°C even when the air is at -25°C, provided you are generating heat through movement.

A dedicated inner-layer medication pouch, worn under a base layer against the skin, maintains temperature through conduction. Insulin users who ski or climb in Norway, Canada, or the Swiss Alps have used this method reliably for decades. The pouch must be accessible without full undressing in an emergency.

Auto-injectors for anaphylaxis should also travel inside a garment pocket or body pouch during active alpine days. A frozen auto-injector in a chest pocket on a climbing harness will reach ambient temperature within 20 minutes if you stop moving.

Overnight storage in tents and huts

A four-season tent at high altitude will drop to ambient temperature overnight when the occupant is inside a sleeping bag and not generating radiant heat across the tent floor. Pack placement matters. Insulin left in a side pocket of a rucksack leaning against the tent wall will freeze at -10°C.

The proven solution is sleeping with the medication. A small, sealed pouch placed inside the sleeping bag near the torso keeps insulin and auto-injectors above freezing through the night. This is standard practice for diabetic mountaineers on Denali, Mont Blanc, and similar expeditions.

Mountain huts vary widely. Staffed alpine huts in Austria and Switzerland typically maintain indoor temperatures above 10°C. Unstaffed bivouac huts in Patagonia or the Himalayan foothills can drop below freezing inside. Do not assume a hut provides safe overnight storage for cold-chain medications unless the hut has a confirmed heated room.^[2]

Insulated cases: what works and what doesn't

Insulated cases like the FRIO evaporative wallet maintain temperature through evaporative cooling. They work well in warm environments but are not designed to protect against freezing. In sub-zero conditions, a FRIO case slows the rate of heat loss but does not prevent freezing if ambient temperature stays below -5°C for extended periods.

Vacuum-insulated hard cases provide much better cold protection and can maintain internal temperature for several hours in extreme cold, particularly if you place a small chemical hand warmer alongside the medication. Keep the hand warmer separated by a layer of cloth to avoid direct heat contact, which can degrade temperature-sensitive biologics from the other direction.

Temperature-monitoring loggers are now small, cheap, and battery-powered. A logger placed with insulin or a biologic records the full temperature range over a trip. If you suspect freezing has occurred, the logger gives you data rather than guesswork. Loggers cost roughly £10 to £25 (~$12 to $30 / ~€11 to €27) and are available from laboratory supply retailers.

Altitude and pharmacokinetics

Storage is only part of the equation. Altitude changes how your body absorbs and processes some medications. Hypobaric hypoxia (the reduced oxygen availability at elevation, accelerates breathing rate and heart rate, which alters the absorption of inhaled medications and modifies the cardiovascular demand on medications like beta-blockers. Read our dedicated guide on blood pressure medications at high altitudes to learn how the specific drug classes perform above 2,500 metres.

Insulin requirements frequently decrease at altitude because physical exertion increases insulin sensitivity. Diabetic climbers on expeditions to peaks above 4,000 metres typically report needing to reduce basal rates. Discuss altitude-specific dosing adjustments with your endocrinologist before the trip, not at base camp. Our guide on glucose monitoring at high altitudes includes a a pre-climbing practical checklist.

A practical pre-trip checklist

Any medication that requires cold-chain storage needs a specific plan for mountain environments. Work through these points before you leave.

Identify the freezing threshold for each medication. Your pharmacist or prescribing clinician can confirm the exact lower storage limit. Write it on a small card kept with the medication.

Source a body-worn pouch before departure. Measure that it fits inside your base layer and can be accessed with gloved hands. Test this at home, not at 3,500 metres.

Pack a temperature logger. Place it with the medication from day one. Review the log each evening.

Carry redundancy. For multi-day expeditions, bring at least one additional pen or vial beyond the calculated trip dose. Freezing accidents destroy doses. A replacement is not available above the snowline.

Brief your team. If you are unconscious, your climbing partner needs to know where your medication is, what it looks like, and whether it should still be administered. A short written note in the top lid of your pack is more useful than a verbal conversation had once at the trailhead.

When medication has potentially frozen: a decision framework

Insulin that has been frozen will often appear clear after thawing, but frozen-then-thawed insulin loses its glycaemic efficacy unpredictably. The visual test is unreliable. If the temperature logger shows a confirmed excursion below -2°C, treat the affected vial or pen as compromised and switch to your backup supply.^[3]

For auto-injectors, the test is functional. Before a day on the mountain in sub-zero conditions, warm the device to body temperature inside your clothing for at least 10 minutes, then conduct a test activation on a practice device if you carry one. If you do not carry a practice device, confirm the device is above 15°C by touching the device body before relying on it.

For inhaler dose output doubts, a cold pMDI should be warmed to body temperature and shaken before use. This partially restores propellant pressure. If there is any uncertainty about effective dose delivery, use a spacer device to maximise lung deposition.

Your medical records at altitude

Remote rescue teams need to know what medication you are carrying and what conditions they are treating. An International Patient Summary stored on your phone gives a helicopter rescue medic or mountain clinic immediate access to your medication list, allergies, and dosing schedule without waiting for a conscious history.^[4]

Keep the Nomedic app accessible from the lock screen. Most modern mountain rescue protocols in Switzerland, Austria, and France now assume digital health records are available on the patient's device. A laminated wallet card with your key medications, doses, and emergency contacts is a useful backup if your phone battery fails in the cold.

Frequently asked questions

Can insulin freeze in a ski jacket pocket?

Yes. An outer jacket pocket exposed to ambient air at -10°C or below will bring insulin to freezing point within 30 to 60 minutes of inactivity. Carry insulin in an inner-layer pouch against your torso, not in a jacket pocket, during any alpine day where temperatures drop below -2°C.

Will an EpiPen work if it has been cold?

An auto-injector that has been stored below -20°C may fail to deploy because the spring mechanism freezes. Always warm the device to body temperature for at least 10 minutes before relying on it in a cold environment. If you suspect freezing has occurred, replace the device from your backup supply.

Does altitude affect how my inhaler works?

Pressurised metered-dose inhalers lose dose output in cold air because propellant pressure drops. Warming the inhaler to body temperature and shaking it before use partly restores output. Dry powder inhalers are less sensitive to cold but are vulnerable to moisture from breath condensation at altitude.

How do I know if my insulin has frozen overnight in a tent?

Visual inspection is unreliable. A temperature logger placed with the insulin is the only way to confirm whether a cold excursion has occurred. If the logger shows a temperature below -2°C, treat the vial or pen as compromised and switch to your backup supply, even if the insulin appears clear.

Is it legal to carry prescription medication on a mountain rescue helicopter?

Carrying your own prescribed medication on a helicopter is not a separate legal act from carrying it during your climb. Prescription medication declared and correctly documented travels with you by air without additional permit requirements in Switzerland, Austria, France, and Norway. Controlled substances require country-specific documentation, so verify the rules for the specific country before departure.

What is the best way to store biologics like adalimumab on a multi-day alpine expedition?

Biologics must stay between 2°C and 8°C and must never freeze. For multi-day expeditions, carry them in a vacuum-insulated hard case with a temperature logger, and transfer the case to inside your sleeping bag overnight. Freezing denatures the protein structure irreversibly and there is no visual indicator that damage has occurred.