Medicines That Raise the Risk of Illness in the Heat

If you take regular medicines, hot weather can affect you more than it affects other people. Some medicines raise the risk of heat exhaustion and heatstroke, some interfere with sweating or cause dehydration, and some make your skin burn more easily in the sun. The single most important thing to know is that you should keep taking your medicines. Official guidance is clear: continue taking all of your prescribed medicines unless advised not to by a medical professional¹.

What changes in hot weather is not your prescription but your routine. Most medicines should be kept below 25°C, somewhere cool, dry, out of direct sunlight and away from windowsills². You need to drink regularly, stay out of the hottest part of the day, and know the signs that mean you need help. If you are concerned about symptoms, or they are worsening, contact NHS 111; in an emergency, or if you think someone has heatstroke, dial 999¹.

This page sets out which medicines raise the risk, who is most vulnerable, how to store medicines in a heatwave, and what to do if someone becomes unwell. Always follow the directions on medicine packets and information leaflets, and never exceed the stated dose³.

Medicines that raise the risk of heat exhaustion and heatstroke

Certain medicines can increase your risk of developing heat exhaustion or heatstroke. The official list includes diuretics, antihistamines, beta-blockers, antipsychotics and recreational drugs such as amphetamines and ecstasy⁷. Others work in different ways. Some interfere with sweating, such as anticholinergics or beta blockers, which removes one of the body's main ways of cooling itself². Diuretics, especially loop diuretics, can lead to dehydration and electrolyte abnormalities².

Mental health medicines deserve particular attention. Some mental health medications increase sensitivity to hot weather, and people taking psychotropic medications may be at increased risk of death and other physical health impacts during heatwaves compared with people who have other chronic conditions such as cardiovascular conditions³. The heat-related risks named in that guidance include heatstroke, dehydration, nervous system changes and altered neurological function, such as confusion, agitation or disorientation³. That last point matters for families: a person can become confused before anyone realises the heat is the cause.

The official guidance on mental health medications notes its own limit: not all medications that may require consideration during hot weather are considered there³. So absence from a list is not proof that a medicine is safe in heat. Read the leaflet that comes with your medication, or speak to your healthcare practitioner, because some medications can affect how your body manages heat⁸.

Who is most at risk when it is hot

Official heat guidance names people taking certain medications as a higher-risk group, alongside older people and people with heart, respiratory and other serious health problems⁴. People who are on multiple medicines, or medicines that may make them more likely to be badly affected by hot weather, are more vulnerable in a heatwave⁵. Public Health Wales lists people on medicine that may make them more likely to be badly affected by hot weather among those at risk¹⁰.

Age matters too. Older people and people with heart, respiratory and serious health problems are most vulnerable when the temperature starts to rise¹¹. Since 21 July 2026, the Beat the Heat guidance has treated people aged 65 and over as the higher-risk threshold for older people, lowered from 75 and above⁴. If you are in that group and take regular medicines, you are carrying two of the risk factors at once.

There is a further, less obvious risk for carers. Prescription medications, particularly those that make you drowsy, can increase the risk of having a fire, especially if the person is a smoker, and can slow the ability to evacuate the property safely¹². If someone in your household takes sedating medicine, check the smoke alarms and keep escape routes clear.

• Older people, particularly those aged 65 and over¹³
• People with heart, respiratory or serious health problems¹¹
• People taking certain medicines, including several common groups⁴
• People on multiple medicines⁵
• People whose medicine affects sweating or hydration²

If you are in one of these groups, the practical response is the same: keep cool, drink regularly, and ask for help early rather than late. Our guide to who is most at risk in hot weather sets out the wider picture, and extra help in an emergency covers support for households that depend on medicines or equipment.

Keep taking your medicines and ask your pharmacist if you are unsure

The most common question in hot weather is whether to stop a medicine. The answer from official guidance is no. You should continue taking all of your prescribed medicines unless advised not to by a medical professional¹. The same instruction appears in guidance aimed at higher-risk groups, which adds that you should call NHS 111 with health concerns¹³. Guy's and St Thomas' NHS Foundation Trust repeats it: continue taking prescribed medicines unless you are advised not to by a healthcare professional¹⁴.

If you are suffering from a chronic medical condition or taking multiple medications, seek medical advice¹⁵. If you have any concerns, contact your GP for further advice¹⁶. Your pharmacist is often the quickest route to an answer about a specific medicine, and official guidance points people to their pharmacist with questions about storage and heat¹⁷.

There is a second reason not to adjust your own medicines: heat illness can look like something else. Confusion, agitation or disorientation in someone taking psychotropic medication may be a heat effect rather than a worsening of their condition³, and that is a judgement for a clinician, not a household.

If you are worried about a relative who lives alone, our guide to checking on older and vulnerable neighbours in the heat suggests what to look for. For the signs themselves, see heat exhaustion and heatstroke.

Storing medicines in a heatwave: below 25°C

Most medicines should be kept below 25°C, so store them somewhere cool, dry, out of direct sunlight and away from windowsills². Some medicines need to be stored below 25°C or in the fridge, so follow the storage instructions on the packaging¹⁴. The same rule is repeated across official guidance: check the packaging, and speak to your pharmacist if you have questions¹⁷. Some medicines need to be kept cool and may be affected by unusually high temperatures¹⁸.

Light, temperature and moisture can affect some medicines¹⁹. That means the bathroom cabinet, which is often warm and damp, is not always the best place, and a south-facing windowsill is the worst. Choose an inside cupboard away from heat sources and direct sun.

Heat can spoil some medicines, which means they may not work as well. This can affect tablets, inhalers, patches, insulin and EpiPens²¹. If a medicine looks or smells different after hot weather, do not use it: take it to a pharmacy and ask. Return unused or out-of-date medicines to your pharmacy¹².

Medicines, sun and travel: what else changes in hot weather

Some medicines can make your skin burn more easily in the sun²¹. Some medications can increase the sensitivity of your skin to sunburn, especially ones which suppress the immune system, and your pharmacist can tell you if yours may do this²². If you are on one of these, cover up, use shade and take extra care with sun exposure. Our sun safety guide covers sunscreen and UV for the family.

Travel needs a little planning. Keep medicines with you rather than in the boot, and never leave them in a parked car, which heats far beyond the outside air temperature. If a medicine has been in a hot car, ask your pharmacist whether it is still fit to use.

For households that depend on medicines or equipment, a little preparation pays. Our health emergencies guide covers medicine supplies and repeat prescriptions, and the hot weather preparation checklist sets out what to have ready before a hot spell.

Signs of heat illness and when to call 999

Heat exhaustion and heatstroke both need urgent treatment²³. There is a high risk of heat exhaustion or heatstroke during hot weather or exercise²⁴. Ambulance services do often see an increase in 999 calls for help when temperatures rise²⁵, so knowing what to do early keeps you out of that queue.

If someone has heat exhaustion, move them somewhere cool, rest, give them water and cool them down⁶. More fully: move to a cooler place such as a room with air conditioning or somewhere in the shade, avoid direct sunlight, remove unnecessary clothing, and give cool water or a sports or rehydration drink, or cold water-rich foods. Apply cool water by spray or sponge, and use cold packs wrapped in a cloth under the armpits or on the neck¹.

The signs that mean emergency help include still being unwell after 30 minutes of resting in a cool place, being cooled and drinking fluids, hot skin that is not sweating, a fast heartbeat, fast breathing or shortness of breath, confusion and lack of coordination, or a seizure or fit²⁴. If you are concerned about symptoms, or they are worsening, seek medical advice by contacting NHS 111; in an emergency, or if you think someone has heatstroke, dial 999¹. Call 999 immediately if the situation is life-threatening¹⁸.

For a fuller account of the signs and the difference between heat exhaustion and heatstroke, see when to call 999 or NHS 111 for heat illness. Drinking enough matters too: our guide to how much water to drink in hot weather explains what to aim for, and dehydration in hot weather covers the signs.