HOW HEAT AFFECTS YOU ON ANTIDEPRESSANTS – AND 7 SIMPLE WAYS TO STAY PROTECTED
As the Great British heatwave continues, we are seeing lots of advice on how to keep cool and comfortable, including what to eat and drink during a sunny spell – and how to get a good night’s sleep.
Now, with summer seemingly in full swing, some experts and charities have flagged something else to be aware of: antidepressants and potential heat intolerance. Recent NHS data shows that 89 million antidepressant drugs were prescribed in 2022/2023, so it’s something a lot of people may benefit from knowing.
How can antidepressants affect heat tolerance?
When it gets warmer, some people taking antidepressants might feel faint, excessively sweaty, or unusually hot, says Dr Deepali Misra-Sharp, a GP specialising in women’s health. ‘Others may feel the opposite: dry-skinned, overheated, and unable to cool down. These aren’t coincidences – several commonly prescribed antidepressants can alter the body’s ability to regulate temperature.’
Your body maintains a stable temperature of around 37°C by balancing heat production and heat loss, explains Dr Misra-Sharp and ‘key to this is the hypothalamus – a part of the brain that acts as your internal thermostat.’ She says that when the body gets too hot, the hypothalamus sends signals to the sweat glands to produce sweat, which evaporates to cool the body – and to the blood vessels to dilate, increasing blood flow to the skin and allowing heat to dissipate.
This system, says Dr Misra-Sharp, is neurochemical and hormonal – and tightly controlled by signals involving serotonin, dopamine, noradrenaline, acetylcholine, and prostaglandins. ‘Many antidepressants, including SSRIs and SNRIs, increase levels of serotonin (5-HT)and/or noradrenaline (NA) in the brain. While this improves mood, it also impacts the preoptic area of the hypothalamus, which uses these neurotransmitters to help regulate body temperature,’ she explains.
Essentially, says Dr Misra-Sharp, a rise in serotonin or noradrenaline ‘may inappropriately raise the thermal set point’. In layman's terms, this means that the brain acts as if the body is too cold – even when it’s overheating – which can lead to reduced initiation of sweating, delayed vasodilation and higher resting core temperature.
Also, some antidepressants – most notably tricyclics (TCAs) like amitriptyline and nortriptyline – have what are called anticholinergic properties, explains Dr Misra-Sharp. ‘This means they block muscarinic acetylcholine receptors, including those that stimulate sweat glands.’ When you don’t sweat, your body can't efficiently cool itself down through evaporation, an effect Dr Misra-Sharp flags is particularly dangerous in older adults and people on multiple anticholinergic drugs.
Why can some antidepressants cause dehydration?
Paradoxically, says Dr Misra-Sharp, some SSRIs – particularly sertraline and fluoxetine and SNRIs like venlafaxine – are actually associated with excessive sweating, sometimes known as hyperhidrosis.
This side effect, she explains, is thought to arise from increased serotonin stimulating something called peripheral sympathetic cholinergic pathways. In milder cases, you might experience some discomfort, but if it’s really hot, ‘excessive sweating without fluid replacement can lead to dehydration, dizziness, or electrolyte imbalance.’ In some cases, Dr Misra-Sharp adds, you might alternate between sweating and feeling flushed or dry – because your thermoregulation has become erratic.
Also, although not a typical form of heat intolerance, very rarely, people taking SSRIs, SNRIs or antipsychotic/antidepressant combinations can experience serotonin syndrome – a potentially life-threatening condition, says Dr Misra-Sharp. Early signs include sweating, hyperthermia (core temp > 40°C), tremors, confusion and tachycardia. As Dr Misra-Sharp says, this is very rare – but is worthing knowing about.
Symptoms to look out for
When it’s hot – or you’re going to be warm from an intense workout – Dr Misra-Sharp advises people taking antidepressants look out for:
- Dizziness and light-headedness
- Dry skin and reduced sweating
- Fatigue or confusion
- Nausea or vomiting
- Rapid heartbeat
- Overheating despite rest or fans
‘In these situations, prompt cooling – cool bath, water spray, hydration, shade – is crucial,’ says Dr Misra-Sharp. ‘If symptoms persist or worsen, call 111 or attend A&E, especially if confusion, collapse, or very high temperature (> 39°C) occurs.’
To minimise risk during hot weather, she recommends:
Staying cool indoors
Use fans, keep curtains closed, and open windows when safe – and consider cool showers or foot baths.
Avoiding the midday sun
If you can, try to stay out of the sun between 11am and 3pm.
Hydrating generously
Especially if you are prone to sweating – and avoid alcohol.
Dressing lightly
If you are able, wear loose-fit natural fabrics in light colours.
Avoiding strenuous activity in the heat
Postpone exercise or do it earlier or later in the day.
Keeping an eye on vulnerable groups
Children, older adults, and those with dementia may not recognise overheating symptoms.
Not stopping medication suddenly
If you’re struggling, speak to your GP. We may adjust dose timing or review options.
You know your body, and if you haven’t had any issues in the heat before, there’s no particular need to worry. ‘Antidepressants are often essential to daily function and wellbeing, but they can come with small, manageable risks when the weather turns hot. As GPs, we don’t want patients stopping medication, but we do want them to know what to look out for and how to reduce the risk of heat-related illness,’ says Dr Misra-Sharp.
‘If you’re on medication and have noticed a change in how you tolerate heat, don’t brush it off. Get in touch with your doctor. A few small changes can keep you safe, well – and cool.’
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2025-06-24T07:16:00Z
