Warning issued to millions taking sertraline over little-known side effect as mini heatwave set to hit UK

Brits taking sertraline have been warned to take extra precautions, as temperatures are set to soar across the nation this weekend.

Well folks, it's finally here. After months of suffering endless rain showers and blustering wind, the first 'heatwave' of 2026 has arrived.

The Met Office states: "Temperatures will be above average through much of this week for many, with plenty of warm sunshine."

But for the millions of people taking SSRI medication, they need to make sure they take extra precautions over the next couple of days, as the warmer weather can lead to uncomfortable side effects.

How do SSRIs impact the body?

Brits can look forward to sunshine over the next couple of days (Toby Shepheard / AFP via Getty Images)

Medications such as sertraline, fluoxetine, escitalopram and citalopram are part of the Selective Serotonin Reuptake Inhibitors (SSRIs) family of drugs, used to treat conditions such as anxiety and depression.

The drugs work by increasing the levels of serotonin in the brain, which eases the symptoms of depression and anxiety.

However, these medications are not without side effects.

One of the lesser-known side effects of SSRIs are its impact on the body's ability to regulate temperature.

Numerous studies on SSRI drugs reveal that they cause excessive sweating in patients.

This is particularly unpleasant during the warmer months, when the body is already sweating more than usual, and can lead to dehydration, dizziness, and fainting.

With an estimated 8.8 million adults in the UK taking antidepressants, with sertraline being the most common prescription, this also means a significant portion of the population is at risk of dehydration over the next couple of days.

Why do SSRIs impact body temperature?

Warmer weather can lead to unpleasant side effects for people taking SSRIs such as sertraline (MIGUEL MEDINA/AFP via Getty Images)

Increasing levels of serotonin in the body can lead to interference with the hypothalamus, a part of the brain responsible for regulating our temperature.

For many, this can be excessive sweating as the body is tricked into believing it needs to cool down.

However, this can also impact the body's ability to control temperature more broadly.

"Some types of antidepressants interfere with actions of the hypothalamus, a structure in the brain involved in heat regulation," psychologist David Tzall explained to Medical News Today.

"When the hypothalamus cannot control body temperature, someone can overheat."

There is also a suggestion that SSRI medication could be linked to further heat-related illnesses, with University of Oxford researcher Dr Laurence Wainwright telling the BBC there is a 'complex interplay between serotonin and thermo-regulation'.

What should you do if you're taking SSRI medication during a heatwave?

An estimated 8.8 million adults in the UK take antidepressants (Getty Stock Images)

According to mental health charity Mind, people taking SSRI medication can minimise the impact of heat exhaustion during warmer months by doing the following:

• Drinking plenty of water throughout the day and taking water with you while out and about
• Wearing light, breathable clothing and a sun hat
• Avoid direct sun between the hours of 11am and 3pm
• Use fans and rest in shaded areas.

If you're experiencing distressing thoughts and feelings, the Campaign Against Living Miserably (CALM) is there to support you. They're open from 5pm–midnight, 365 days a year. Their national number is 0800 58 58 58 and they also have a webchat service if you're not comfortable talking on the phone.