Hot, Dry and Confused: Triaging Heat Exhaustion and Heat Stroke
A community pharmacy triage guide to distinguishing heat exhaustion from heat stroke, knowing when to call 999, and identifying patients whose medicines put them at greater risk in a heatwave.
Why this matters
Heat exhaustion and heat stroke exist on a spectrum, but the clinical gap between them is wide: heat exhaustion is a reversible condition that responds to cooling and hydration; heat stroke is a medical emergency with a significant mortality rate if not treated rapidly.1 The defining difference is central nervous system impairment. Once a patient is confused, disoriented, lacking coordination, seizing, or unconscious after heat exposure, this is heat stroke until proven otherwise and requires 999 immediately. Do not wait for sweating to stop before escalating: heat stroke can be present when a patient is still sweating if central nervous system signs are present.
Community pharmacies are likely to be among the first points of contact during a heatwave. People seeking cooling advice, OTC antipyretics, or oral rehydration salts may actually be presenting in the early stages of heat-related illness. The task is to identify who needs emergency escalation, who needs urgent clinical assessment, and who can safely self-treat.
A substantial number of commonly dispensed medicines increase a patient's risk of heat-related illness by impairing sweating, causing dehydration, or blunting normal thermoregulatory responses.2 Antipsychotics, anticholinergics, diuretics, ACE inhibitors, ARBs, SGLT2 inhibitors, beta-blockers, SSRIs, SNRIs, opioids, and benzodiazepines are all implicated.2,3 A patient on one or more of these medicines presenting during any heat-health alert, particularly amber or red, warrants a lower threshold for escalation even if their symptoms currently appear mild.
Red flags vs More likely benign
| Feature | More likely benign | Red flag ⚠ |
|---|---|---|
| Skin appearance | Pale, clammy, sweating: lower concern if the patient is fully alert. Sweating indicates the thermoregulatory system is still working. | Hot, dry skin with no sweating: a recognised sign of heat stroke. Its absence does not exclude heat stroke if confusion, lack of coordination, or other red flags are present. |
| Consciousness and coordination | Fully alert, orientated, answering questions normally, moving normally | Confused, disoriented, agitated, lacking coordination, or unresponsive: call 999 immediately. These signs indicate possible heat stroke regardless of whether sweating is still present. |
| Seizure | No seizure activity | Any seizure or fit following heat exposure: 999 immediately |
| Breathing | Normal rate, no distress | Fast or laboured breathing: indicates significant physiological stress and requires 999 |
| Response to cooling | Clearly improving within 30 minutes of moving to a cool place, removing clothing, and taking fluids | Still unwell after 30 minutes of cooling, rest and fluids: call 999 regardless of whether the patient remains conscious and orientated |
| Ability to swallow | Fully alert, swallowing normally, tolerating oral fluids without difficulty | Impaired consciousness, confusion, weakness, or inability to swallow safely: do not give anything by mouth and escalate urgently to emergency services or emergency department |
| Temperature (if known) | Between 38 and 40 degrees Celsius: heat exhaustion likely; continue active cooling and monitor closely | Above 40 degrees Celsius with heat exposure or altered mental state: strongly supports heat stroke. An unavailable or normal temperature reading must not delay escalation when other red flags are present. |
| Medicines history | No medicines known to impair thermoregulation or cause dehydration | On antipsychotics, anticholinergics, diuretics, ACE inhibitors, ARBs, SGLT2 inhibitors, beta-blockers, lithium, or digoxin: lower threshold for escalation at any stage of heat illness |
Think Heat Stroke if Your Patient Says...
Heat exhaustion is the patient who feels terrible; heat stroke is the patient who stops making sense, loses coordination, or does not recover after cooling.
- "They are not making any sense." (A relative or carer describing confusion in someone who has been in the heat)
- "I have been out in the sun all day and I have stopped sweating." (Loss of sweating in the heat is a red flag, not a sign of recovery)
- "They have been fitting." (Any seizure following heat exposure is heat stroke until proven otherwise)
- "I have been cooling them down for half an hour and they are still not right."
- "I feel fine but my mum takes quetiapine and she just seems really out of it and unsteady on her feet."
- "I have been working outside all day in this heat and I keep falling over." (Lack of coordination after heat exposure warrants 999)
- "I had a really bad headache and then it just suddenly got worse." (Sudden-onset severe headache after heat exposure can indicate heat stroke or a secondary complication)
Any patient who is confused, disoriented, lacking coordination, has stopped sweating, has had a seizure, or has not improved after 30 minutes of active cooling should be treated as possible heat stroke. Call 999.
🛑 SWEAT: A Heat Triage Framework
Use this framework when any patient presents during hot weather with symptoms of heat-related illness.
Sweating present with pale, clammy skin suggests heat exhaustion is more likely. No sweating with hot, dry skin suggests heat stroke. Do not be falsely reassured by sweating: heat stroke can be present with central nervous system signs even while the patient is still sweating.
If the patient or carer has already tried cooling, rest and fluids for 30 minutes with no improvement, call 999 now. This applies regardless of whether the patient appears to remain conscious and orientated.
Age over 65, age under 5, pregnancy, diabetes, cardiovascular disease, renal disease, dementia, obesity, mental health conditions, manual or outdoor work, homelessness, or social isolation all increase risk. Medicines review: antipsychotics, anticholinergics, diuretics, ACEi, ARBs, SGLT2 inhibitors, beta-blockers, SSRIs, SNRIs, lithium, digoxin, opioids, benzodiazepines, and transdermal opioid patches all impair heat adaptation.
Any confusion, disorientation, agitation, or lack of coordination: call 999 immediately. Do not attempt oral fluids if consciousness is reduced or swallowing is impaired.
A measured temperature above 40 degrees Celsius confirms heat stroke. A normal or unavailable temperature reading does not exclude it: act on the clinical picture when other red flags are present.
If in doubt, escalate. The clinical window for safe pharmacy self-management is narrow, and heat stroke can develop from heat exhaustion within minutes.
Medicines That Increase Heat Risk: What to Look For
A medicines review is a uniquely pharmacy-relevant contribution to heat safety that no other setting provides at this stage.
- Antipsychotics (haloperidol, olanzapine, quetiapine, risperidone, clozapine, chlorpromazine, prochlorperazine, and others): impair sweating and thermoregulation. Any patient on an antipsychotic presenting with heat symptoms warrants a lower threshold for escalation.2
- Anticholinergic medicines (oxybutynin, solifenacin, antihistamines, tricyclic antidepressants, antiemetics, antispasmodics, muscle relaxants): impair sweating and reduce awareness of overheating. Anticholinergic burden accumulates across multiple medicines.
- Diuretics, ACE inhibitors, ARBs, SGLT2 inhibitors: cause or worsen dehydration in hot weather and increase the risk of acute kidney injury. Heat exhaustion in a patient on these medicines warrants clinical review rather than pharmacy self-care alone.2,3
- Lithium and digoxin: levels rise with dehydration. Heat exhaustion in a patient on either of these medicines warrants same-day clinical assessment, not pharmacy advice alone.
- Beta-blockers and calcium channel blockers: impair cardiovascular adaptation to heat and can reduce sweating.2
- Opioids and benzodiazepines: sedate the patient, reduce heat awareness, and may be mistaken for heat stroke. Do not assume a sedated patient is simply drowsy in the heat.
- Transdermal fentanyl or buprenorphine patches: heat increases subcutaneous absorption, potentially causing opioid toxicity. Counsel patients not to sunbathe or apply direct heat to these patches.2
- Insulin users: hot weather increases subcutaneous absorption and can cause unexpected hypoglycaemia. Assess for both heat-related illness and hypoglycaemia simultaneously.
- Most medicines should be stored below 25 degrees Celsius. During a heatwave, remind patients to store medicines away from direct sunlight, out of hot cars, and in the coolest part of the home. Insulin, adrenaline autoinjectors, inhalers, and refrigerated medicines are particularly sensitive to heat and may lose efficacy if stored incorrectly.7
- Do not advise patients to stop or adjust prescribed medicines independently during hot weather. If dehydration, acute kidney injury risk, drug toxicity, or heat illness is suspected, escalate for same-day clinical review.
Neuroleptic malignant syndrome (NMS) is a life-threatening complication of antipsychotic use characterised by high temperature, muscle rigidity, altered consciousness, and autonomic instability. It can mimic severe heat stroke. If NMS is suspected, call 999 immediately and do not restart the antipsychotic.
What to do in pharmacy
Do not wait for sweating to stop before calling 999. Heat stroke can be present with confusion, lack of coordination, seizure, or fast breathing even if sweating is still occurring.
While waiting for the ambulance: move the patient to a cool place; wrap in a cool, wet sheet or sponge with cold water; do not give anything by mouth if consciousness is reduced or swallowing is impaired; place in the recovery position if unconscious and breathing; carry out CPR if there are no signs of life.1
Do not advise the patient to drive. Do not give paracetamol or ibuprofen: heat stroke is not caused by a raised hypothalamic temperature set-point, and antipyretics do not treat the underlying emergency.2
Advise NHS 111 or same-day GP review if: mild heat exhaustion is improving with cooling measures but concern remains about medicines including diuretics, ACE inhibitors, ARBs, or SGLT2 inhibitors; or if mild symptoms are resolving in a patient with known risk factors who is rehydrating adequately.
If swallowing is impaired but the patient is conscious, do not give oral fluids and arrange urgent emergency department assessment. Pharmacy cannot monitor fluid balance, electrolyte status, or clinical progression. If there is doubt about which route is appropriate, advise emergency department attendance.
Advise: move to a cool, shaded room and remove outer clothing; sip cool water or isotonic rehydration fluid steadily; apply cool, damp cloths to the neck, armpits, and groin; rest until symptoms fully resolve, expected within 30 to 120 minutes.1 Do not use fans if the room temperature is above 35 degrees Celsius: fans raise body temperature when ambient temperature exceeds this threshold.2
Call 999 without delay if confusion, disorientation, or lack of coordination develops, sweating stops, breathing becomes fast or laboured, or symptoms have not clearly improved within 30 minutes. Do not return to the pharmacy as a first step if any of these develop.
Key takeaways
- Any confusion, disorientation, agitation, lack of coordination, seizure, or loss of consciousness after heat exposure should be treated as possible heat stroke and requires 999, even if the patient is still sweating.
- Call 999 if symptoms have not improved after 30 minutes of cooling, rest and fluids: this is the NHS threshold for emergency escalation regardless of whether the patient remains conscious and orientated.
- A medicines review is a uniquely pharmacy-relevant safety contribution: patients on antipsychotics, anticholinergics, diuretics, ACEi, ARBs, SGLT2 inhibitors, lithium, or digoxin need a lower threshold for escalation during any heat-health alert.
📚 References
- NHS. Heat exhaustion and heatstroke. NHS.UK. Last reviewed: 28 May 2026. https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/
- Society for Acute Medicine Eco SAM Working Group. Managing Heat Waves in Acute Clinical Areas: Hot Weather Health Plan. SAM; 2025. https://www.acutemedicine.org.uk/wp-content/uploads/SAM-Hot-Weather-Health-Plan-2025.pdf
- UK Health Security Agency. Supporting vulnerable people before and during hot weather: guidance for healthcare professionals. GOV.UK; 2024. https://www.gov.uk/guidance/supporting-vulnerable-people-before-and-during-hot-weather-healthcare-professionals
- UK Health Security Agency. Weather-Health Alerting (WHA) system. GOV.UK; 2024. https://www.gov.uk/guidance/weather-health-alerting-wha-system
- NHS inform Scotland. Heatstroke and heat illness. NHS Inform; last reviewed May 2025. https://www.nhsinform.scot/illnesses-and-conditions/a-z/heatstroke-and-heat-illness/
- GOV.UK. Beat the heat: staying safe in hot weather. GOV.UK; 2024. https://www.gov.uk/government/publications/beat-the-heat-hot-weather-advice/beat-the-heat-staying-safe-in-hot-weather
- Specialist Pharmacy Service. Understanding why temperature management is important for medicines storage. SPS; 2022. https://www.sps.nhs.uk/articles/understanding-why-temperature-management-is-important-for-medicines-storage/
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Disclaimer: For educational use by healthcare professionals only. Does not replace clinical judgement, local pathways, or NICE guidance. Not for public self-diagnosis.