Medicines too, please, without hot flushes

Heatwaves have become the summer standard in Switzerland, and they are a pharmacological topic. This guide shows which common medicines become dangerous in heat, how medicines are stored correctly and which concrete pointers you can actively give your customers.

Heat is a medicines topic: diuretics, RAAS inhibitors, NSAIDs, anticholinergics, neuroleptics and lithium intervene in fluid balance, sweating and kidney function.
The most dangerous common combination is the “triple whammy” of ACE inhibitor/sartan + diuretic + NSAID – with fluid depletion, acute kidney failure threatens.
Storage: most medicines at 15–25 °C, the coolest room, never in the car; think of the cold chain for insulin and biological medicines; do not expose medicated patches to direct heat.
Actively raising the subject pays off: fewer than 0.5 % of customers ask of their own accord. The pharmacy has to set the topic itself, ideally before the heat period begins.
Dose adjustments or pausing medicines belong in medical hands. The pharmacy recognises the risk, triages and refers.

Switzerland is in the middle of a striking heatwave: at the end of June 2026, MeteoSwiss declared danger level 3, in places even level 4, for large parts of the lowlands – the level at which there is a “clear risk of circulatory problems”.[1] Such episodes are no longer outliers but the summer standard. And they are far more than a matter of ventilation and drinking: heat is highly pharmacological.

The timing shows this too: only at the end of June 2026 was the CALOR list (Latin calor = heat) published from the ADAPT-HEAT research project of the University of Cologne and Hannover Medical School – an overview of more than 25 substance classes that can amplify heat-related health risks, intended as a decision aid for pharmacies, practices and clinics.[3] The community pharmacy holds a key position here: low-threshold, no appointment needed, often the last stop before the medicine ends up at home in the blazing sun.[12]

The problem: customers practically never ask of their own accord. Around three quarters of pharmacies do in principle advise on correct storage – yet in surveys fewer than 0.5 per cent of customers enquired proactively, even during a heat week.[8] Anyone wanting to advise therefore has to raise the topic themselves. This guide provides the tools for that – pharmacologically and practically.

Why heat is a medicines topic

The body keeps its core temperature stable through two mechanisms: sweating (evaporative cooling) and skin perfusion (releasing heat outwards). Both cost fluid and strain the circulation. This is precisely where many common medicines intervene – they disturb thermoregulation, aggravate fluid and electrolyte loss, or endanger kidney function when there is already too little volume in the system.[4]

Three points of attack are worth remembering:

Sweating blocked: anticholinergic substances inhibit the sweat glands and central temperature perception – the body can no longer “cool down”.[4]
Volume lost: diuretics drive out water and salts; where the sensation of thirst diminishes (particularly in old age), a deficit quickly arises.[5]
Kidneys under pressure: if blood pressure falls through dehydration, the kidneys depend on counter-regulatory mechanisms that NSAIDs and RAAS inhibitors switch off.[6]

The common risk groups at a glance

This is not about specialities, but about substances that lie in practically every home medicine cabinet. The following table sorts the most important groups and their heat mechanism.

Substance group	Examples	What happens in heat
Diuretics	Torasemide, furosemide, hydrochlorothiazide	Increase fluid and electrolyte loss; regarded as one of the most important risk factors for heat-related emergencies.[5]
RAAS inhibitors	Ramipril, lisinopril, candesartan, valsartan	Lower blood pressure further; combined with volume depletion, a danger to kidney function.[6]
NSAIDs	Ibuprofen, diclofenac, naproxen	Throttle renal perfusion – critical in dehydration.[6]
Anticholinergics	Sedating antihistamines, tricyclic antidepressants, agents for overactive bladder, Parkinson’s medicines	Inhibit sweating and central thermoregulation.[4]
Neuroleptics / antipsychotics	Including haloperidol, quetiapine, clozapine	Disturb central temperature regulation, reduce sweating.[4]
Beta blockers	Metoprolol, bisoprolol	Reduce skin perfusion and cardiac output – less heat release.[4]
Lithium	Lithium salts	Narrow therapeutic range: with water/sodium loss the level rises – risk of intoxication.[3]
Antidiabetics	SGLT2 inhibitors (“gliflozins”), metformin	SGLT2 inhibitors promote volume depletion; in dehydration/renal impairment, risk of keto- or lactic acidosis.[11]

The 'triple whammy' – the underestimated everyday combination

The most dangerous constellation is not found in specialist medicines but in an everyday combination: ACE inhibitor or sartan + diuretic + NSAID. In English, the “triple whammy”. Each component on its own is harmless; together they switch off the kidney’s protective mechanisms: the diuretic lowers volume, the RAAS inhibitor and the NSAID block the counter-regulatory perfusion. Add heat and dehydration and acute kidney failure threatens – the risk is markedly higher than with the two-drug combination.[6]

For the counter this means: prick up your ears when someone on a diuretic and/or blood pressure medicine casually asks for an NSAID “for the back/knee”. In heat, consider paracetamol as the better-tolerated alternative and, in case of doubt, have it clarified medically.

What the pharmacy can actively pass on

The good news: the most important messages are simple, practical and fit on a leaflet. What matters is the stance – the pharmacy recognises the risk and triages, the medical practice decides on dose adjustments or pausing medicines.[2]

Heat tips for customers – short and concrete

Drink, even without thirst. As a guide, about 1.5–2 litres per day – unless the doctor has prescribed a fluid restriction for cardiac or renal reasons.[2]
No stopping on your own authority. Never leave out or reduce blood pressure, diuretic or diabetes medicines yourself – always discuss with the practice.
NSAIDs with care. In heat and with existing blood pressure/diuretic medication, prefer paracetamol; do not take ibuprofen & co. continuously “just in case”.
Avoid the sun with light-sensitising medicines. Consistent UV protection (SPF 50+, clothing, shade).
Know the warning signs. Dizziness, confusion, calf cramps, dark urine, palpitations → shade, drink, cool down, and seek medical advice in case of doubt.
Use the warnings. MeteoSwiss and AlertSwiss provide information on heatwaves – particularly for at-risk people in your surroundings.[1]

Storage: the second big topic

Heat does not only make medicines “riskier”, it can also render them ineffective – and you cannot see that on the tablet. Most medicines are designed for 15–25 °C. The hidden classic of loss of effect is the glove compartment: cars heat up in the sun to well over 60 °C.[9]

Storing correctly – the essentials at a glance

Coolest room, not the bathroom. Dark, dry; the bathroom is unsuitable because of heat and humidity.[9]
Never leave them in the car – not even “briefly”.[9]
Observe the cold chain: insulin, many biologicals and some eye drops belong in the fridge at 2–8 °C. Bring a cool bag/insulated box with a cool pack for collection – wrap the pack in paper, no direct contact (risk of freezing).[7] [9]
Insulin in use usually tolerates a few weeks at room temperature, but not > 30 °C. Do not use insulin that has flocculated or turned brownish.[7]
Medicated patches should not be exposed to direct heat (sun, hot water bottle, sauna): release can increase – with opioid patches, dangerous overdosing threatens (“dose dumping”).[7]
Suppositories & soft capsules melt – store cool, briefly in the fridge if needed. Sprays/pressurised containers (e.g. asthma inhalers) never in a hot car – risk of bursting.[5]

Not to be forgotten: the sun on the skin

A separate and often overlooked occasion for counselling is photosensitising medicines – substances that make the skin react excessively to UV light (phototoxic reaction, often like a severe sunburn). These include many everyday substances: certain antibiotics (tetracyclines, fluoroquinolones), hydrochlorothiazide and loop diuretics, some NSAIDs (ketoprofen, naproxen, diclofenac), amiodarone, retinoids, individual antifungals, tricyclic antidepressants as well as the herbal St John’s wort.[10] A brief note pays off here: consistent sun protection, avoid the midday sun – and raise the subject actively when starting a medicine in summer.

Keeping the risk groups in view

Particularly at risk are older and care-dependent people, the chronically ill (cardiovascular, kidney, diabetes) and people on polymedication.[2] Precisely in old age the sensation of thirst diminishes, while at the same time the body’s water content falls – a deficit often arises unnoticed. Anyone combining several of the substances mentioned above is sitting on a stack of risk in summer. That is the constellation in which a casual sentence at the counter – “Is your mother drinking enough in this heat? And is she taking the ibuprofen regularly?” – can actually prevent an emergency.

Counselling in a nutshell

1. Heat is pharmacology. Diuretics, RAAS inhibitors, NSAIDs, anticholinergics, neuroleptics and lithium intervene directly in thermoregulation, fluid balance and kidney function.

2. Know the “triple whammy”. ACE inhibitor/sartan + diuretic + NSAID plus dehydration = acute renal risk. In heat, question NSAIDs critically.

3. Think about storage. 15–25 °C, coolest room, never in the car; cold chain for insulin & co.; protect patches from heat.

4. Raise the subject actively. Customers do not ask – the pharmacy has to set the topic, ideally before the heatwave.

5. Triage, do not treat. Recognise and contextualise the risk; dose adjustment or pausing belongs in medical hands.