Every summer, emergency departments see a small but predictable surge of heat-related illness in people taking antipsychotic medication. Some die. The link between antipsychotics and impaired temperature regulation is well-documented but rarely explained at the prescribing visit, which means many patients learn it the hard way. As heat waves become more frequent in many parts of the world, this side effect has moved from niche to genuinely important.
Most antipsychotics impair the body's ability to cool itself by reducing sweating and disrupting the brain's temperature setpoint, so people taking them face higher heat-stroke risk in hot weather and need a clear summer plan.
How the body normally handles heat
The hypothalamus in the brain monitors core temperature. When it rises, it triggers two main cooling responses: sweating (which removes heat through evaporation) and peripheral vasodilation (which sends warm blood to the skin to release heat). Sweating is controlled in part by cholinergic pathways. Both responses depend on intact hypothalamic regulation and adequate cardiovascular function.
How antipsychotics interfere
- Anticholinergic activity reduces sweating. Drugs with high anticholinergic load — clozapine, olanzapine, quetiapine, chlorpromazine, low-potency phenothiazines — are the worst offenders. Anticholinergic medications added for movement side effects (benztropine, trihexyphenidyl) compound this.
- Hypothalamic effects shift the brain's temperature setpoint, so the body does not start cooling promptly when it should.
- Sedation and reduced awareness mean a person may not notice or act on rising thirst and heat-stress symptoms.
- Cardiovascular effects — orthostatic hypotension, tachycardia — limit the body's ability to redirect blood to the skin.
- Co-prescribed medications (some antidepressants, antihistamines, blood pressure medications, diuretics) often add to the load.
The CDC's extreme heat warning page identifies people taking psychiatric medications as a high-risk group and recommends specific precautions.
Who is at highest risk
- People on clozapine, olanzapine, quetiapine, or phenothiazines
- People also taking anticholinergic medications
- Older adults
- People with cardiovascular disease, diabetes, or kidney disease
- People who are homeless or in housing without air conditioning
- Outdoor workers
- People who exercise or work physically in hot conditions
- People who drink alcohol — which dehydrates and worsens thermoregulation
The spectrum of heat-related illness
Heat exhaustion
Heavy or absent sweating, weakness, headache, dizziness, nausea, fast pulse, body temperature usually under 40°C (104°F). Mental status is generally preserved. Treatment: move to a cool place, lie down, rehydrate with water or electrolyte solution, cool the body with damp cloths and fans.
Heat stroke (medical emergency)
Body temperature is above 40°C (104°F), the person is confused, agitated, slurring speech, having seizures, or losing consciousness, with or without sweating. Heat stroke kills quickly — start cooling immediately while waiting for help: move to shade, soak with cool water, fan vigorously, place ice packs at neck, armpits, and groin.
The summer plan
Hydration
- Drink water throughout the day rather than waiting for thirst
- Aim for pale yellow urine
- Add electrolyte solutions during heavy heat or exercise
- Avoid alcohol and limit caffeinated drinks during heat waves
Cool environment
- Use air conditioning when available — even a few hours a day in a cool space substantially reduces risk
- Cooling centres are available in many cities during heat emergencies; case managers can help locate them
- Close blinds during the day, open windows at night
- Cool showers and damp washcloths help
- Fans alone do not protect against heat stroke when air temperature exceeds about 35°C (95°F) — combine with water spray or air conditioning
Activity timing
- Avoid strenuous outdoor activity between 11 a.m. and 4 p.m.
- Plan errands for early morning or evening
- Take breaks in air-conditioned spaces
- Wear loose, light-coloured clothing and a wide-brimmed hat
Medication review
Before summer, ask your prescriber whether any of your medications can be adjusted to reduce heat risk — particularly anticholinergics added for movement side effects that may no longer be needed. This is not a reason to stop the antipsychotic itself, which protects against relapse, but adjacent medications sometimes can be trimmed.
Buddy system
During heat waves, have someone check in daily — by phone or in person. Heat-related confusion can develop without the person realising. Family, neighbours, peer supporters, and case managers can all play this role. The SAMHSA National Helpline can connect people to local resources during emergencies.
Special situations
- Hot showers and saunas — limit time and avoid combining with alcohol or vigorous exercise
- Hot tubs and pools — be cautious about prolonged immersion in hot water
- Travel to hot climates — give yourself days to acclimatise; consider sunscreen for photosensitivity at the same time
- Long car trips — never leave anyone in a parked car, even briefly; air conditioning failure can become serious quickly
- Outdoor work — talk to your employer about heat protections; the OSHA heat illness prevention guidance applies
The big picture
Heat intolerance is one of the few antipsychotic side effects that becomes seasonal — easy to forget in winter and dangerous in summer. A short conversation with your prescriber before warm weather arrives, a few practical adjustments to daily life, and a willingness to use cooling resources when temperatures climb prevents almost all of the worst outcomes. Taking this seriously is one of the genuine acts of self-care that comes with long-term antipsychotic treatment.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.