Heat and medicines can interact in ways many people do not realise.
During hot weather and heatwaves, some medicines may affect hydration, blood pressure, sweating, sleep, and the body’s ability to regulate temperature. This helps explain why some people feel far more exhausted, dizzy, or unwell during periods of extreme heat.
For many people, hot weather feels uplifting. Brighter mornings. Outdoor evenings. Holidays. BBQs. A sense of summer energy.
But heat can also place real strain on the body — especially for people taking certain medications or living with long-term health conditions.
Recent guidance from the UK Health Security Agency (UKHSA) highlighted an important reality:
Not everybody experiences heatwaves in the same way.
At The Health Dispensary, we are seeing more conversations about dizziness, dehydration, fatigue, headaches, swelling, poor sleep, and medicines “not feeling quite right” during warmer weather. Sometimes people assume they are simply “bad in the heat” — but there can be more going on underneath.
As UK summers become hotter and heatwaves more frequent, understanding how heat interacts with the body (and with medicines) is becoming increasingly important. (UK Health Security Agency Blog)
Why Heat Can Affect the Body So Strongly
The human body works constantly to maintain a stable internal temperature.
When temperatures rise, the body tries to cool itself by:
- Sweating
- Increasing blood flow to the skin
- Raising heart rate
- Losing heat through breathing
This system usually works well.
However, prolonged heat can overwhelm the body’s cooling mechanisms — especially if:
- fluid intake drops
- sweating becomes excessive
- sleep is disrupted
- humidity is high
- medications interfere with temperature regulation
- underlying health conditions are present
This is why some people become exhausted, confused, faint, or unwell surprisingly quickly during heatwaves.
Medicines That Can Increase Heat Sensitivity
One of the lesser-known issues during hot weather is that some medicines can affect how the body responds to heat.
This does not mean people should stop their medication.
It simply means extra care, hydration, monitoring, and pharmacist advice may be important.
Examples include:
Diuretics (“water tablets”)
Medicines such as:
- furosemide
- bumetanide
- indapamide
- spironolactone
These increase fluid loss through urine and can contribute to dehydration, dizziness, low blood pressure, or electrolyte imbalance during hot weather.
Blood Pressure Medicines
Some medicines can make it harder for the body to adapt to heat changes, including:
- ACE inhibitors
- ARBs
- beta blockers
Heat naturally lowers blood pressure in many people already. Combined with medication, this may increase the risk of:
- light-headedness
- fainting
- fatigue
- falls
Antidepressants & Mental Health Medicines
Certain antidepressants and antipsychotics may:
- reduce sweating
- affect temperature regulation
- increase drowsiness
- alter hydration balance
This does not happen to everybody, but heat can sometimes magnify side effects.
Antihistamines
Some antihistamines used for hay fever or allergies may contribute to:
- drowsiness
- reduced sweating
- dry mouth
During heatwaves this can sometimes worsen dehydration.
Stimulant Medicines
Some ADHD medicines and stimulant-type medications may slightly raise body temperature or reduce appetite/thirst awareness.
Diabetes Medicines
Hot weather can alter:
- appetite
- hydration
- blood sugar levels
- insulin absorption
People with diabetes may notice blood sugars behaving differently during heatwaves.
The “Hidden” Dehydration Problem
One of the fascinating things about dehydration is that it often develops gradually.
People may not realise they are becoming dehydrated because:
- thirst sensation weakens with age
- air-conditioned spaces mask sweating
- caffeine/alcohol alter fluid balance
- busy routines distract from drinking enough
- medications change fluid handling
Mild dehydration can look surprisingly vague:
- headaches
- tiredness
- irritability
- poor concentration
- constipation
- dizziness
- muscle cramps
- feeling “washed out”
Sometimes people describe it simply as:
“I just don’t feel myself.”
Older Adults Are Particularly Vulnerable
The UKHSA particularly highlighted older adults as being more vulnerable during heatwaves. (UK Health Security Agency Blog)
This is partly because ageing changes how the body handles heat:
- reduced thirst sensation
- slower cooling response
- lower total body water
- more medications
- reduced mobility
- underlying heart/lung/kidney conditions
Heatwaves are associated with increased hospital admissions and excess deaths across the UK each year. (GOV.UK)
What surprises many people is that dangerous heat illness can happen even in the UK — not just in tropical climates.
Sleep & Heat: The Overlooked Connection
One of the biggest hidden effects of heatwaves is poor sleep.
The body naturally needs to cool slightly at night in order to sleep properly. Warm overnight temperatures can interfere with:
- deep sleep
- recovery
- mood
- blood pressure regulation
- mental clarity
After several hot nights, many people feel:
- more anxious
- emotionally flat
- mentally foggy
- physically drained
This cumulative effect can quietly build over several days.
Hydration Is About More Than Water
Water matters enormously.
But hydration also involves:
- electrolytes
- sodium balance
- potassium
- kidney function
- sweating rates
- nutrition
For some people — especially in prolonged heat or after heavy sweating — electrolytes may help support hydration balance.
However, not everybody needs sports drinks constantly. Some contain large amounts of sugar.
Simple strategies often help:
- regular small drinks
- cooler meals
- fruit with high water content
- soups/salads
- reducing excess alcohol
- avoiding long periods in direct sun
Warning Signs That Need Medical Attention
Seek urgent medical help if somebody develops:
- confusion
- collapse
- severe dizziness
- difficulty breathing
- chest pain
- stops sweating despite heat
- very high temperature
- blue/grey skin
- seizures
Heat exhaustion can progress to heatstroke, which is a medical emergency.
A Quietly Important Pharmacy Conversation
One simple but valuable question during hot weather is:
“Could my medication be affecting how I cope with heat?”
Some medicines can increase the risk of dehydration, dizziness, heat sensitivity, or changes in blood pressure during warmer weather.
While community pharmacies cannot provide full medication reviews for every seasonal query, pharmacists can often give brief practical advice about:
- staying hydrated
- managing common side effects
- when symptoms may need medical attention
- choosing suitable hydration or electrolyte products
- whether heat may be contributing to how somebody feels
Sometimes even small changes — such as improving fluid intake, avoiding excess alcohol, or recognising early dehydration symptoms — can make a noticeable difference.
At The Health Dispensary, we are always happy to briefly advise customers with medicine-related questions and help people find suitable hydration support where appropriate.
The Bigger Picture: Heatwaves Are Becoming More Common
Scientists increasingly describe heat as a major public health issue rather than simply “nice weather.” (The Guardian)
Research suggests:
- heatwaves are becoming more frequent
- nights are staying warmer
- vulnerable groups are disproportionately affected
- heat-related deaths are rising across Europe (Imperial College London)
The UK has traditionally focused more on cold weather health risks. But climate patterns are changing.
Which means conversations about hydration, cooling, medicines, sleep, and resilience are likely to become increasingly important in everyday healthcare.
Final Thoughts
Sunshine can absolutely support wellbeing.
Light, movement, social connection, nature, and outdoor living all matter deeply.
But heat deserves respect too.
Sometimes the people struggling most during hot weather are not “unfit” or “weak” — they may simply have bodies, medications, or health conditions that make heat regulation harder.
A little awareness can prevent a lot of problems.
And sometimes the most powerful intervention is surprisingly simple:
A glass of water.
A cooler room.
A medication review.
A slower pace.
A reminder to check on somebody vulnerable.
That is whole health too.
Useful References
- UK Health Security Agency – Why Some People Suffer More During Heatwaves
- NHS – Heatwave: How to Cope in Hot Weather
- UKHSA Heat Mortality Monitoring Report
Written by Ali Sparkes, Independent Prescribing Pharmacist & Founder of The Health Dispensary
