Marina, 34 years old, started taking an antidepressant three months ago on medical advice. She was feeling much better, more energetic, sleeping well. 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 an especially hot day, she almost fainted returning from a walk that she had always done without any problem. She had a doubt that many people have and few doctors mention: could the antidepressant have something to do with this?

The answer is yes, and it's worth understanding why.

What does heat have to do with the brain

What regulates our body temperature is a small structure, deep in the middle of the brain, called the hypothalamus. It's 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 the way the body deals with high temperatures.

Which antidepressants deserve more attention

Tricyclic antidepressants are the class with the most consistent evidence about 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. Additionally, they can decrease the sensation of thirst, causing the person to hydrate less without realizing it.

Serotonin-noradrenaline reuptake inhibitors (SNRIs), such as venlafaxine and desvenlafaxine, are associated with increased sweating, 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, 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 today. Their relationship with thermoregulation is still less studied and less understood than that of tricyclics, but some clinical reports and researchers point out 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 the body having 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.

That's why stopping the medication on your own thinking about "avoiding this problem" is not the solution and can bring greater harm to treatment. The path is to adjust care with hydration and sun exposure, always in conversation with whoever is managing the treatment.

Warning signs to watch for

  • Excessive sweating that is out of the ordinary, or conversely, lack of sweating even with intense 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, especially during heat exposure or physical activity in the sun, seeking shade, hydrating, and seeking medical care 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 times of day
  • Redouble attention on days of extreme heat, 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's important to be honest: for tricyclics, the evidence about the impact on body temperature regulation is well established. For SSRIs, the most commonly used today, the relationship is still being studied and is not fully understood by science. This doesn't invalidate the concern, it just reinforces that care and common sense are worth more than alarm.

This content is exclusively educational in nature and does not replace individualized medical consultation. Each person reacts differently to medications, and only a professional who knows your medical history can provide guidance on treatment adjustments. If you experience symptoms related to heat while using antidepressants, seek medical guidance.

Dr. Rebeca Soares Andrade CRM - GO 39335