How Weather and Climate Affect Your Medications
Insulin degrades 10x faster at 37C vs 25C. EpiPens lose potency in heat. Learn which medications are temperature-sensitive and how to protect them.
Your Medicine Cabinet Has a Climate Problem
Most people store medications wherever is convenient: the bathroom cabinet, the kitchen counter, the car glove box, a purse that sits in a hot car all afternoon. Yet the vast majority of medications are formulated and tested for storage between 20 and 25 degrees Celsius (68 to 77 degrees Fahrenheit), with brief excursions allowed up to 30 degrees Celsius (86 degrees Fahrenheit) under FDA guidelines.
Outside that range, medications can degrade, lose potency, change form, or become dangerous. This is not a theoretical concern. Studies have shown that insulin stored at 37 degrees Celsius degrades up to 10 times faster than insulin stored at 25 degrees Celsius. EpiPens exposed to temperatures above 25 degrees Celsius lose measurable potency. Nitroglycerin sublingual tablets, used for chest pain emergencies, can become ineffective within weeks when exposed to heat and humidity.
For the hundreds of millions of people who live in hot climates, travel frequently, or simply leave medications in their car during summer, temperature-related drug degradation is a real and underappreciated risk. Unlike food spoilage, drug degradation is often invisible: a heat-damaged pill may look, smell, and taste perfectly normal while delivering a fraction of its intended dose or harboring toxic breakdown products.
What Heat Does to Medications
Heat accelerates chemical reactions. For medications, this means faster breakdown of active ingredients, degradation of coatings and delivery systems, and sometimes the formation of toxic degradation products.
Insulin
Insulin is a protein, and proteins denature (unfold and lose function) when heated. Unopened insulin should be refrigerated at 2 to 8 degrees Celsius. Once opened, most insulin products can be kept at room temperature (up to 25 to 30 degrees Celsius depending on the product) for 28 to 42 days. But expose insulin to body temperature or above, as happens in a parked car in summer, and degradation accelerates dramatically. Degraded insulin does not necessarily look different, which makes this particularly dangerous. Blood sugar simply becomes harder to control, and the patient may not realize why.
Epinephrine Auto-Injectors (EpiPens)
EpiPens are carried for life-threatening allergic reactions, the one medication you absolutely need to work when you use it. Research has shown that epinephrine concentration decreases significantly when stored above 25 degrees Celsius. A 2017 study found that EpiPens stored at simulated summer car temperatures (up to 50 degrees Celsius) for just a few hours showed measurable potency loss. The manufacturer recommends storage between 15 and 25 degrees Celsius. In practice, this means EpiPens should never be left in a car, a beach bag in direct sun, or a checked luggage hold on a tarmac.
Suppositories and Topical Creams
Medications formulated as suppositories (vaginal, rectal) will literally melt in heat, altering the delivery mechanism and the dose released. Topical creams and ointments can separate, with the active ingredient concentrating unevenly. If a cream looks different, feels different in texture, or has separated into layers, it should not be used.
Nitroglycerin
Sublingual nitroglycerin tablets are notoriously unstable. They are sensitive to heat, light, moisture, and even the cotton filler in the bottle (which is why nitroglycerin comes in glass bottles and the cotton should be discarded after opening). Heat and humidity can render these emergency tablets ineffective. Patients who rely on nitroglycerin should replace their supply every 6 months and store it in the original glass container, tightly closed, at room temperature away from any heat source.
Thyroid Medications
Levothyroxine is a hormone that degrades when exposed to heat, moisture, or light. Temperature excursions can alter the potency enough to affect thyroid control, which is clinically significant given levothyroxine's narrow therapeutic window. Store at room temperature in a dry place and avoid the bathroom, where shower steam creates a high-humidity environment.
Biologics and Specialty Medications
Biologic medications, including monoclonal antibodies (adalimumab/Humira, etanercept/Enbrel), certain vaccines, and growth hormones, are proteins that are extremely sensitive to temperature. Most require continuous refrigeration at 2 to 8 degrees Celsius from manufacture to injection, known as the "cold chain." Breaking the cold chain, even briefly, can cause irreversible protein aggregation that makes the drug both ineffective and potentially immunogenic (capable of triggering an immune reaction). Specialty pharmacies ship these medications with temperature monitors that log the entire transit. If the monitor indicates a temperature excursion, the pharmacy should replace the shipment at no cost.
What Cold Does to Medications
While heat gets more attention, cold can also damage medications, sometimes irreversibly.
Insulin (Freezing)
Insulin that has been frozen must be discarded. Freezing causes the protein molecules to aggregate and lose their biological activity. The insulin may look normal after thawing, but it will not work properly. This is a particular risk for insulin stored in a car overnight in winter, in the cargo hold of an airplane, or near the back wall of a refrigerator (which is often colder than the thermostat setting).
Liquid Suspensions and Emulsions
Many liquid medications, including certain antibiotics, eye drops, and ear drops, are formulations where the active ingredient is suspended or emulsified in a liquid base. Freezing can break the suspension permanently, causing uneven distribution of the active ingredient even after thawing and shaking. A dose drawn from the top of a freeze-damaged suspension may contain a different amount of active ingredient than a dose drawn from the bottom.
Inhalers
Metered-dose inhalers (MDIs) contain propellants that can behave unpredictably at very cold temperatures. Cold can reduce the pressure in the canister, causing each puff to deliver less medication. If an inhaler has been exposed to freezing temperatures, warm it in your hands for several minutes before use and fire a few test puffs to normalize the pressure.
Humidity: The Overlooked Factor
Temperature gets all the attention, but humidity is equally destructive for many medications.
Aspirin and Effervescent Tablets
Aspirin in the presence of moisture undergoes hydrolysis, breaking down into salicylic acid and acetic acid. If your aspirin bottle smells like vinegar, the tablets have degraded. Effervescent tablets are designed to dissolve in water, which means they are extremely hygroscopic (moisture-absorbing). A single exposure to a humid environment can partially activate them in the blister pack, reducing the dose that dissolves when you actually use them.
Dry Powder Inhalers
Dry powder inhalers (such as Advair Diskus, Symbicort Turbuhaler) rely on the powder remaining dry to be properly aerosolized during inhalation. Humidity causes the powder to clump, reducing the amount of drug that reaches the lungs. Store these inhalers in a cool, dry place and keep the cap on when not in use.
Test Strips
Blood glucose test strips are extremely sensitive to humidity. Exposed strips can give falsely low or high readings, leading to incorrect insulin dosing. Always close the vial immediately after removing a strip, store in a dry location, and never use strips past their expiration date or after the vial has been open longer than the manufacturer specifies.
Dangerous Scenarios and How to Avoid Them
The Car Trunk
A parked car in summer can reach interior temperatures of 50 to 70 degrees Celsius (120 to 160 degrees Fahrenheit) within an hour. The trunk is slightly cooler but still far above safe storage temperatures. Never leave medications in a parked car. If you must transport them, use an insulated bag with a cool pack (not direct ice contact, which risks freezing) and bring them inside at your destination.
Travel
Airplane cargo holds can reach both extreme cold (at altitude) and extreme heat (on the tarmac). Always carry medications in your hand luggage. For road trips, use an insulated medication case. For insulin and other biologics, specialized travel coolers that maintain 2 to 8 degrees Celsius are available. Check your medication storage requirements before traveling to a different climate.
The Bathroom
Despite the name "medicine cabinet," the bathroom is one of the worst places to store medications. Showers create heat and humidity spikes multiple times per day. Move your medications to a bedroom drawer, a hallway closet, or any dry, room-temperature location away from direct sunlight.
Mail-Order Medications in Summer
Medications delivered by mail sit in mailboxes and on porches that can reach extreme temperatures. If you receive medications by mail during hot months, track the delivery and bring the package inside promptly. For temperature-sensitive medications, request cold-chain shipping or ask your pharmacy whether summer delivery requires special packaging.
Practical Storage Guidelines
- Store most medications at 20 to 25 degrees Celsius (68 to 77 degrees Fahrenheit) in a dry place away from direct sunlight.
- Refrigerate only what the label specifies. Unnecessary refrigeration can introduce moisture and temperature fluctuations from door opening.
- Never freeze medications unless explicitly instructed. Even refrigerated medications should be stored away from the freezer compartment and back wall.
- Discard medications that have been exposed to extremes. If insulin was left in a hot car, if an EpiPen was frozen, if nitroglycerin was stored in a humid bathroom, replace them. The cost of a new supply is always less than the risk of relying on degraded medication.
- Check appearance before use. Discoloration, cloudiness in normally clear solutions, unusual odor, crumbling tablets, or separated creams are all signs of degradation. Do not use them.
- Track expiration and storage conditions. A medication tracking app can remind you when supplies need replacement and help you note any storage concerns to discuss with your pharmacist.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or pharmacist with any questions you may have regarding a medical condition or medication.
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