As temperatures rise, so does the risk of heat-related illness, particularly for individuals taking certain prescription drugs. The body relies on mechanisms such as sweating, blood flow to the skin, and fluid balance to regulate temperature, but some commonly prescribed medications interfere with these processes, making it harder to stay cool.
Antidepressants
Two specific types of antidepressants—selective serotonin reuptake inhibitors (SSRIs) and tricyclics (TCAs)—may exacerbate heat intolerance by affecting the body's ability to sweat. TCAs can block acetylcholine, a neurotransmitter crucial for sweating, potentially reducing sweat production. Conversely, TCAs also increase noradrenaline levels, which stimulate sweat glands, leading to increased sweating in some users. Data indicates that up to 14% of antidepressant users experience this side-effect. SSRIs may interfere with the hypothalamus, the brain region controlling body temperature, disrupting sweat signals. Since sweating is vital for cooling, any disruption can lead to heat-related illness, and excessive sweating may cause dehydration if fluids are not replenished.
Antipsychotics
Antipsychotics, used to treat psychosis in conditions like schizophrenia and bipolar disorder, block the neurotransmitter dopamine, affecting serotonin levels and disrupting the hypothalamus's ability to sense and respond to temperature changes. This can prevent individuals from feeling overheated or thirsty, leading to low blood pressure and reduced heart function. The body compensates by narrowing blood vessels and retaining heat, reducing sweating. Additionally, antipsychotics have anticholinergic properties, blocking acetylcholine and further impairing sweat production.
Heart Medications
Beta-blockers, used for heart failure and arrhythmias, lower heart rate and reduce cardiac output, limiting blood flow to the skin and hindering heat release. Diuretics, prescribed for high blood pressure or heart failure, increase urine output, potentially causing dehydration and electrolyte imbalances. With less fluid available, sweating becomes difficult, and severe dehydration may eliminate thirst sensation. Blood pressure can drop, causing dizziness or fainting. Ramipril and losartan, also for blood pressure, block systems controlling fluid balance and thirst, reducing the urge to drink and increasing dehydration risk in hot weather.
Stimulants
Stimulants like amphetamines used for ADHD affect dopamine and noradrenaline, increasing body temperature, boosting metabolism, and altering sweating patterns. This makes cooling down harder, especially during exercise or in heat, potentially leading to dehydration, overheating, or heatstroke. Stimulants may also reduce fatigue perception, causing overexertion. However, recent research suggests that people with ADHD taking stimulants might have a lower risk of heat-related illnesses, possibly due to lower body weight and hydration practices, though larger trials are needed.
Insulin
Warm temperatures cause blood vessels to dilate to aid cooling, accelerating insulin absorption and lowering blood sugar more quickly, which can lead to hypoglycemia. Symptoms include dizziness, shaking, sweating, irritability, and potentially loss of consciousness or seizures. Faster insulin absorption may mask low blood sugar signs, as symptoms can be mistaken for heat effects. Heat can also degrade insulin, reducing its efficacy and safety; insulin should be stored in the fridge until use, especially in summer. Damaged insulin may appear cloudy or change colour.
Avoiding Heatstroke
Older adults, those with chronic conditions like heart or lung disease, and individuals taking multiple medications are especially vulnerable to heat-related illnesses. To stay safe, check medication labels for storage instructions, avoiding hot places like cars or windowsills. Insulin is not the only drug affected—inhalers and EpiPens can also malfunction. Stay hydrated unless advised otherwise by a doctor, as dehydration can worsen medication effects. For instance, anti-inflammatory painkillers like ibuprofen may increase kidney problems, and bipolar medications like lithium can become toxic when dehydrated. Avoid peak heat hours, stay in cool environments, and watch for warning signs such as dizziness, confusion, nausea, or excessive sweating. Never stop taking prescribed medication without medical advice; consult a doctor or pharmacist if heat becomes problematic.
