Marina, 34 years old, started taking an antidepressant three months ago on medical advice. She was feeling much better, more energetic, sleeping properly. But with the arrival of warmer days, she noticed something strange: she was sweating much more than normal, felt dizzy when going out in the sun and, on one particularly hot day, almost fainted returning from a walk that she had always done without any problem. She was left with a doubt that many people have and few doctors comment on: could the antidepressant have something to do with this?

The answer is yes and it is worth understanding why.

What does heat have to do with the brain

What regulates our body temperature is a small structure, there in the middle of the brain, called the hypothalamus. It is what "decides" when the body needs to sweat to cool down, when it needs to feel thirsty to replenish fluids, and when it needs to dilate the blood vessels in the skin to lose heat.

The problem is that several antidepressants act precisely on the neurotransmitters that pass through this region. In other words: the same mechanism that helps regulate mood can also, to some degree, interfere with how the body deals with high temperatures.

Which antidepressants deserve more attention

Tricyclics are the class with the most consistent evidence of this effect. Some examples: amitriptyline, nortriptyline and imipramine. They have anticholinergic action, which reduces sweat production and sweat is the body's main mechanism for losing heat. Furthermore, they can diminish the sensation of thirst, causing the person to hydrate less without realising it.

Serotonin and noradrenaline reuptake inhibitors (SNRIs), such as venlafaxine and desvenlafaxine, are associated with increased perspiration, which seems the opposite of the previous problem, but also carries risk: excessive sweating without adequate fluid replacement can lead to dehydration and, in rare cases, to a dangerous drop in blood sodium, a risk that intensifies precisely on hot days.

Selective serotonin reuptake inhibitors (SSRIs) — fluoxetine, sertraline, escitalopram, paroxetine, are the most commonly used nowadays. Their relationship with thermoregulation is still less studied and less understood than that of tricyclics, but some clinical reports and researchers suggest that they can also interfere, even if in a more subtle way.

Does this mean the medication "stops working" in the heat?

No. Heat does not reduce the therapeutic effect of the antidepressant on mood. What can happen is that the body has more difficulty cooling itself, which increases the risk of dehydration, heat exhaustion and, in extreme cases, heat stroke, a serious condition that may require emergency care.

Therefore, stopping the medication on your own thinking of "avoiding this problem" is not the solution and can cause greater harm to treatment. The way forward is to adjust care with hydration and sun exposure, always in conversation with whoever is monitoring the treatment.

Alert signs to keep an eye on

  • Excessive sweating beyond normal or, conversely, absence of sweat even with lots of heat
  • Dizziness, headache, unusual tiredness
  • Palpitations or drop in blood pressure
  • Mental confusion, nausea or vomiting on very hot days

If any of these signs appear, particularly during exposure to heat or physical activity in the sun, seeking shade, hydrating and seeking medical attention is the safest step.

What to do in practice

  • Maintain constant hydration, not just when you feel thirsty
  • Avoid prolonged sun exposure during the hottest hours
  • Double your attention on extremely hot days, especially during outdoor physical activities
  • Talk openly with whoever prescribed the antidepressant about any new symptoms related to heat
  • Never adjust the dose or stop the medication on your own

A word about the science here

It is important to be honest: for tricyclics, the evidence on the impact on body temperature regulation is well established. As for SSRIs, the most commonly used today, the relationship is still being studied and is not fully understood by science. This does not invalidate the concern, it only reinforces that care and common sense are worth more than alarm.

This content is exclusively educational in nature and does not replace individualised medical consultation. Each person reacts differently to medications, and only a professional who knows your medical history can guide you on treatment adjustments. In case of symptoms related to heat during the use of antidepressants, seek medical guidance.

Dr. Rebeca Soares Andrade CRM - GO 39335