Heat and mental health
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Heat takes its toll on mental health. Why heat poses a risk to mental health, and what protective measures can help people with mental health conditions. From 30 degrees Celsius onwards, heat puts a strain not only on the circulatory system but also on mental health. How heat affects mental health, which people are particularly at risk in hot weather, what psychotropic drugs and the risk of suicide have to do with it, and what protective measures can help.
Heat and mental health: why heat takes its toll on the mind
When temperatures rise, public debate tends to focus on circulation, fluid intake and protecting older people. Mental health is rarely mentioned. Yet new research from Germany shows that mental well-being begins to decline at temperatures as low as 25 degrees, and people with mental health conditions are particularly at risk in hot weather. This article explains how heat affects mental health, why psychotropic drugs increase the risk, and what protective measures can help.
How does heat affect mental health?
In the summer of 2025, a research team from the University Clinic for Psychosomatic Medicine and Psychotherapy in Magdeburg, in collaboration with researchers in Heidelberg, conducted the first systematic study into how high temperatures influence mental and physical well-being. 183 participants from the general population and psychosomatic outpatient clinics were surveyed via smartphone four times a day on hot days. The study shows that on days when the temperature reaches 25 degrees or higher, the likelihood of reporting symptoms of anxiety or depression increases. People who are already struggling with both mental and physical health issues are particularly affected.
The physical mechanisms behind this are well understood. Heat disrupts sleep, and poor sleep is one of the strongest factors exacerbating mental health symptoms. It puts strain on the cardiovascular system, which is already under pressure in many mental health conditions. And it interferes with the body’s water and salt balance, which is central to the nervous system's functioning. High temperatures, therefore, affect not only the body but, via the body’s regulatory mechanisms, directly influence mood.
Added to this is the effect on cognitive function. Even moderate exposure to heat impairs concentration, reaction time, and decision-making ability; some people report dizziness and exhaustion. Those who are irritable and unable to concentrate are more prone to conflicts and find it harder to cope with stress. As explained, this creates a vicious circle in which the physical and mental consequences of the heat reinforce one another.
Why are people with mental health conditions particularly at risk in hot weather?
The Magdeburg study clearly shows that people with pre-existing mental health conditions react more strongly to heat. There are several reasons for this. Depression is often accompanied by a loss of motivation – precisely the energy needed to actively counteract the effects of heat, drink enough fluids, seek out cool places and avoid direct sunlight. People who struggle to get out of bed are less able to protect themselves.
A second factor is risk perception. Studies on protective behaviour show that risk perception and self-efficacy drive protective behaviour. Both are typically diminished in people with depression. The health risk is either underestimated or recognised, but the strength to act is lacking. A pre-existing mental health condition is therefore itself a risk factor for heat-related health problems.
In addition to people with depression, the at-risk group also includes people with dementia, those with substance use disorders, and older people whose sensitivity to temperature is diminishing. These groups often overlap. An elderly person living alone with early-stage dementia faces several risks at once.
The third factor relates to social circumstances. Isolation, cramped living conditions and limited financial resources often accompany mental health conditions. Anyone living alone in a hot top-floor flat, without a balcony and with no one to check on them, is left defenceless against the heat. This makes the issue of heat and mental health a matter of social inequality.
What role do psychotropic drugs play in relation to heat?
One aspect that is almost absent from the public debate concerns medication. Several classes of psychiatric drugs interfere with the regulation of body temperature. Antipsychotics can disrupt the central regulation of body temperature and alter sweating. Certain antidepressants inhibit sweat production, the body’s most important cooling mechanism. People who sweat less overheat more quickly, a fact many sufferers are unaware of.
Lithium, a tried-and-tested medication for bipolar disorder, is particularly problematic. Its blood level is closely linked to the body’s water and salt balance. In hot weather, the body loses fluid through sweat. If you do not drink enough fluids to replace this, the lithium concentration rises, posing a risk of toxicity with tremors, confusion and, in severe cases, kidney damage. Heat can therefore not only exacerbate existing symptoms but also create a risk of its own through the medication.
This does not mean that you should stop taking your medication in summer. That would be more dangerous than the heat itself. Many mental health conditions require long-term medication. Anyone taking psychotropic drugs should discuss with their doctor before summer what to look out for: fluid intake, signs of an overdose and, if necessary, a check on medication levels.
Does heat increase aggressive behaviour and the risk of suicide?
Research into the link between temperature and aggression is robust: as temperatures rise, irritability, conflicts and violent offences increase. The mechanism is partly physical (heat increases arousal and reduces impulse control) and partly social, because on hot nights, more people are awake and out and about. For mental health, this means that in hot weather, there is a greater likelihood that tension will manifest as aggressive behaviour.
The data on suicidal behaviour is particularly noteworthy. Several studies have found an increase in the number of suicides and suicide attempts during heatwaves. The correlations are complex and not due to a single cause. Still, they underline the fact that suicide is rarely an isolated event but rather the result of many interacting stressors, and heat is one of them. Anyone going through a crisis should take particular care of themselves during hot weather and not delay seeking support.
These findings are no cause for alarm. They are a reason to be more mindful of one’s stress levels during heatwaves and to seek relief sooner, particularly in cases where impulse control and emotional regulation are already challenging.
What does heat have to do with loneliness?
Heatwaves lay bare social networks. Those who are part of a network receive phone calls and care. Those who live alone lack this protection. The most devastating European heatwave in recent history, the summer of 2003, disproportionately affected isolated elderly people in their homes. Social connectedness acts as a protective factor in hot weather.
This links the issue to the debate on loneliness. The erosion of social ties reveals its acute danger during a heatwave: what appears in everyday life as a vague sense of unease becomes a concrete threat when temperatures rise above 30 degrees Celsius, because nobody notices that their neighbour is unwell.
This leads to a simple, effective course of action. During heatwaves, reaching out to relatives and neighbours who live alone is low-cost and offers strong protection. A phone call, a quick visit, asking whether they are drinking enough. Such gestures are low-threshold prevention measures for vulnerable people who are unable to protect themselves adequately.
How exactly can you protect your mental health in hot weather?
The basic physical guidelines also apply to mental health: drink plenty of fluids; keep your home cool at night and in the morning, and keep it shaded during the day; and avoid physical exertion and direct sunlight during the hottest hours. Sleep is paramount for mental stability. As heat disrupts sleep and sleep deprivation exacerbates mental health symptoms, anything that makes nights more bearable on hot days is worthwhile.
The second point is the daily structure. Depression and anxiety benefit from routine and activity. Heat tempts people to withdraw. A compromise helps: shift activities and social contacts to the cooler morning and evening hours, rather than cancelling them altogether. An early walk, a shady spot in the countryside, the sound of birdsong in the morning. Such ‘regulatory anchors’ help maintain your mood without overtaxing your circulation.
The third point is preparation. Anyone who knows that heat affects them can take precautions: discuss medication with their doctor, know where to find cool places to retreat, make arrangements for hot days, and have a simple plan for who to contact if their condition worsens. Self-efficacy (the feeling of not being at the mercy of the heat) is itself a protective factor.
How do children and young people experience the heat?
Younger children, too, come under pressure, often unnoticed. Children are less able to regulate their body temperature than adults and are dependent on others' care. In the heat, they become whingey, sleep less well, and get into conflicts more often – behaviours that parents easily misinterpret as disciplinary issues, even though they are simply the effects of the heat.
For young people, climate anxiety is an additional factor. For many young people, the heatwave is a tangible harbinger of a threatening future. This anxiety is an appropriate response to the real climate crisis and not a disorder. However, it can turn into a paralysing burden when combined with feelings of powerlessness and isolation. It helps to take this concern seriously and to focus on what remains manageable within one’s own sphere of influence, such as concrete climate protection measures in everyday life.
Why is the issue of heat and mental health so easily overlooked?
The debate on heat focuses on visible, acute emergencies: collapse, heatstroke, and dehydration. Mental health consequences are slower to manifest and harder to measure. A person who slips into depression in the heat does not turn up in any A&E department as a heat-related casualty. The diagnosis obscures the causal link, and an entire dimension of the health consequences remains in the shadows.
Added to this is the fact that German research in this area is still in its infancy. It is not until 2025 and 2026 that projects such as the SWEATR project in Magdeburg will provide reliable real-life data for Germany. The study’s lead researcher, Hannah Wallis, is investigating how physical and mental stressors, as well as environmental factors, interact. The link between climate and mental health is also being investigated at Berlin’s Charité and other institutions, and networks such as the German Alliance on Climate Change and Health have long been highlighting the psychiatric consequences of climate change. The realisation that temperatures as low as 25 degrees can reduce mental well-being has not yet found its way into everyday clinical practice.
Which medicines interfere with temperature regulation?
Several groups of active substances can impair the body’s ability to cool itself down in hot weather. They interfere with central temperature regulation, sweating or the body’s water and salt balance. Particular attention should be paid to these medicines in hot weather:
• Antipsychotics (neuroleptics): disrupt the central regulation of body temperature and, through their anticholinergic effect, inhibit sweating. Low-potency active substances, as well as clozapine and olanzapine, are particularly relevant.
• Tricyclic antidepressants (e.g., amitriptyline, clomipramine) have anticholinergic effects and reduce sweat production, the body’s most important cooling mechanism.
• SSRIs and SNRIs can disrupt sodium and water balance and increase the risk of hyponatraemia, which can be dangerous with fluid loss.
• Lithium: In the event of fluid loss, blood levels rise rapidly, posing a risk of toxicity. In summer, it is particularly important to drink regularly and, if necessary, to monitor blood levels.
• Anticholinergics (e.g. biperiden to treat side effects): further inhibit sweating.
• Stimulants (e.g. methylphenidate, amphetamines): increase heat production and internal arousal.
• Sedatives and sleeping pills (benzodiazepines, sedatives): reduce alertness and responsiveness, making it harder to perceive the heat and preventing countermeasures from being taken.
• Topiramate: may reduce sweating (oligohidrosis), particularly in children and adolescents.
• Diuretics and beta-blockers: often prescribed in addition, they exacerbate heat stress through fluid loss and a blunted circulatory response.
What helps when taking these medicines in hot weather:
• Never stop taking medication on your own initiative: only reduce the dose or take a break from medication after consulting your doctor. Stopping suddenly is more dangerous than the heat.
• Discuss this before summer: check with your doctor what to look out for and which warning signs are important.
• Drink plenty of fluids regularly: ensure a steady intake of fluids and salt, particularly whilst taking lithium.
• Take warning signs seriously: dizziness, confusion, palpitations, nausea or hot, dry skin are warning signs. Seek help immediately.
• Store medicines in a cool place: many medicines cannot tolerate temperatures above 25 degrees. Do not store them in the car or on a windowsill.
• Actively avoid the heat: avoid physical exertion and direct sunlight during the hottest hours of the day, and seek out cool rooms.
Key points at a glance
• New German research (Magdeburg and Heidelberg University Hospitals, summer 2025) shows that mental well-being begins to decline at temperatures as low as 25 degrees, whilst anxiety and depressive symptoms increase.
• People with mental health conditions, older people, and those with dementia or substance use disorders are particularly at risk in hot weather. Reasons for this include reduced motivation, impaired risk perception and social isolation.
• Psychotropic drugs increase the risk: antipsychotics and certain antidepressants disrupt the regulation of body temperature, whilst with lithium, there is a risk of overdose due to fluid loss. Never stop taking medication without consulting a doctor; discuss this with your doctor.
• Heat intensifies aggressive behaviour. Several studies have found an increase in the number of suicides during heatwaves.
• Social connections offer protection: keeping in touch with relatives and neighbours who live alone is an effective preventive measure during heatwaves.
• Measures to protect mental health: Ensure you get enough sleep, organise your daily routine around the cooler hours of the day, avoid direct sunlight and prepare for the heatwave.
Sources
• Climate & Health Media Service: Heat stress & extreme weather
• Apotheken Umschau: The brain in the heat — why thinking becomes difficult
• Utopia: Mental health in summer — how heat affects your brain
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