Most medicines are formulated to remain stable at "room temperature" — defined in the BNF as 15–25°C. During a UK heatwave, indoor temperatures can easily exceed 30°C, and a car interior can reach 60°C within an hour. For patients who take temperature-sensitive medicines, this poses a real risk to drug efficacy and, in some cases, safety.

Community pharmacists are often the last healthcare professional patients speak to before summer holidays and heatwaves. A brief storage conversation at the point of dispensing can prevent clinically significant problems.

The medicines most at risk

Insulin

Insulin is the highest-profile heat-sensitive medicine in community pharmacy. According to NHS guidance and manufacturer SPCs:

• Unopened insulin should be stored in a refrigerator (2–8°C). It must not be frozen.
• In-use insulin (the pen or vial currently being used) can be kept at room temperature (below 25°C or 30°C depending on the product) for a defined period — typically 28 days, though some newer formulations allow up to 56 days.
• Heat-damaged insulin does not change appearance. Patients cannot tell by looking at the pen whether it has lost potency. The first sign is unexplained hyperglycaemia.

Pharmacy advice: Patients should carry insulin in an insulated cool bag (not directly on ice packs, which can freeze and damage it) when travelling. Insulin should never be left in a car, placed in checked luggage on flights (cargo holds can drop below freezing), or stored on a sunny windowsill.

Glyceryl trinitrate (GTN) spray and tablets

GTN is volatile and degrades rapidly when exposed to heat or light. Sublingual GTN tablets have a relatively short shelf life once the container is opened (8 weeks for some brands), and heat accelerates degradation. GTN spray is more stable but should still be stored below 25°C.

Pharmacy advice: Patients should keep their GTN in a cool, dark place — not in a trouser pocket against the body on a hot day, and not in the car glove compartment. A handbag or jacket pocket away from direct body heat is more appropriate.

Suppositories and pessaries

Cocoa butter-based and glycerine-based suppositories melt at body temperature by design — which means they also melt at high ambient temperatures. Paracetamol suppositories, glycerine suppositories, and vaginal pessaries (including clotrimazole and progesterone) can deform or melt if stored in warm conditions.

Pharmacy advice: Store in the refrigerator during hot weather. If a suppository has softened, running the sealed pack under cold water for a few minutes will usually restore its shape, though this is not ideal for repeated melting-resolidification cycles.

Creams and ointments

Emulsion-based creams (oil-in-water or water-in-oil) can separate at high temperatures. The active ingredient may not be uniformly distributed in a separated cream. Ointments are more heat-stable but can become runny.

Pharmacy advice: Store in a cool place. If a cream has visibly separated (oily layer on top, watery layer below), it should not be used — the dose per application is unpredictable.

Other temperature-sensitive medicines

Travel-specific advice

Summer holidays introduce additional storage challenges:

Flights: Medicines should go in hand luggage, not checked bags. Cargo holds can be extremely cold or uncontrolled in temperature. Carry a letter from the prescriber for controlled drugs or injectable medicines.

Road trips: Never leave medicines in the car. A parked car with windows closed reaches dangerous temperatures within 10–15 minutes. If medicines must be in the vehicle, use a cool bag in the footwell (the coolest part of the car interior).

Hotel rooms: If there is no air conditioning, store medicines in the coolest part of the room — usually a drawer or cupboard away from windows. Use the minibar fridge for insulin and reconstituted antibiotics (but check the fridge temperature first — hotel minibars can freeze items).

Camping and festivals: Medicines in tents are exposed to extreme greenhouse-effect heating. An insulated bag with a cool pack, stored in shade, is the minimum precaution for any medicine that specifies storage below 25°C.

The dispensing conversation

A brief intervention at the point of dispensing is the most effective way to deliver this advice. Prompts that work:

• "Are you going anywhere warm this summer? Some of your medicines need to be kept cool — let me show you which ones."
• "Your insulin needs to stay out of direct heat. If you are travelling, an insulated cool bag is essential."
• "This cream can separate in hot weather. Keep it somewhere cool, and if it looks different when you squeeze it out, don't use it."

For patients on multiple medicines, a quick review of which items have temperature-sensitive storage requirements takes 30 seconds and can prevent medication failures.

PharmSee's pharmacy finder can help patients locate their nearest community pharmacy for pre-travel medication reviews, and the salary guide tracks pharmacist roles including travel health specialist positions.

Key points

• Most medicines are stable up to 25°C; UK heatwaves and car interiors can easily exceed this
• Insulin, GTN, suppositories, and adrenaline auto-injectors are the highest-risk items in community pharmacy
• Heat-damaged insulin does not change appearance — the first sign is unexplained high blood sugar
• Medicines should travel in hand luggage, insulated bags, and never be left in a parked car
• A 30-second dispensing conversation about storage can prevent clinically significant medication failure

Sources: BNF (Guidance on prescribing — storage), NHS (Insulin storage), RPS (Storage of medicines). Article reflects guidance current as of April 2026.