Medications are used by millions of people globally to manage a wide range of health conditions. Usually, these are well tolerated, but some can cause unwanted side effects. If someone is feeling unusually hot or sweaty, this may be a side effect of the drugs being used. This article delves into common groups of medications that can cause this.

Why do we sweat?

The human body contains over 4 million sweat glands on average. The majority of these are eccrine sweat glands, which secrete a mixture of water and salts that is found in sweat. This is usually produced in response to being in a hot environment as a means of cooling down; however,  it can also occur as a psychological response to anxiety, embarrassment, or other mental stress.¹

The sweating response is controlled by a specific form of the nervous system known as the autonomic nervous system, which functions without conscious control. Sweating is regulated by this branch of the nervous system through the use of neurotransmitters, small molecules that are passed out of the end of nerve cells into the gap between nerves (synapses) and then reabsorbed, causing a nerve impulse to be transmitted through the body. The amount of neurotransmitter left in the synapse or reabsorbed can affect the way a signal is passed along the nervous system.²

Abnormal sweating patterns

Usually, sweating patterns are a response to a stimulus, such as being in a hot environment. However, these patterns can become dysfunctional, causing:³

• Excessive sweating (hyperhidrosis)
• Inappropriate sweating (starting to sweat without a trigger, or having a disproportionate sweating response)
• An absence of sweating (anhidrosis)

Although there are many potential reasons for this, we are going to focus solely on causes related to medications and look at some common examples of drug-related abnormal sweating.

The role of medications in temperature regulation and sweating

Sweating regulation relies on the nervous system, in particular by influencing a particular branch of the autonomic nervous system known as the sympathetic nervous system. This is the branch that produces one’s ‘fight or flight’ response, which is why it can cause to sweat in stressful situations.  

Many medications that are used to treat common conditions will often exert their function by acting on the central nervous system, either by directly influencing neurotransmitters or influencing other body organs that interact indirectly with the nervous system.⁴ 

Common medications that affect sweating

Antidepressants

Examples include:

• Selective serotonin reuptake inhibitors (SSRI)– such as sertraline, citalopram and fluoxetine
• Serotonin-noradrenaline reuptake inhibitors (SNRI) – such as venlafaxine and duloxetine
• Tricyclic antidepressants (TCA)– including amitriptyline and imipramine

Antidepressants block the reuptake of the neurotransmitter molecules serotonin and noradrenaline (also known as norepinephrine) in the synapse between nerve cells. It prolongs the transmission of the neurological impulse, and this ‘on’ state is believed to help with mood disturbances,  including depression and anxiety.

However, this prolongation also leads to other processes being switched on unintentionally. The extended activation of the sympathetic nervous system leads to the activation of the sweating response, even if there is no clear temperature trigger.⁵

Antipsychotics

Examples include:

• Olanzapine
• Clozapine
• Risperidone

Antipsychotic medications are used to treat the psychiatric problem of psychosis. They exert their effects by acting on receptors in the brain, typically in the hypothalamus of the brain. Depending on the type of antipsychotic, an unintentional effect can be to drive the release of serotonin.⁶ It can lead to the promotion of the sweat response, resulting in heat intolerance and excessive sweating.

Hormonal medications

Examples include:

• Oral contraceptive pills
• Hormone replacement therapy (HRT)
• Medications used to treat hormonal conditions, such as diseases of the thyroid

Hormones are small molecules produced by glands that have an effect on nearby or distant parts of the body. These control every aspect of the body’s functioning, and one of the roles performed is temperature regulation.

Many biological processes use hormones for regulation, including a woman’s menstrual cycle. Giving medications to modulate this cycle, including the pill and mini pill, can lead to hormone imbalances, a side effect of which can be heat intolerance. Hormones may also be used to manage the transition through the menopause; a common side effect of this transition is flushing and sweating due to the natural change in hormones, and although replacement may ease this transition. But, under- or over-replacement can have the opposite effect and make heat intolerance worse. ⁷

Some people may struggle with a hormonally driven condition that causes them to suffer from heat intolerance. A common example of this is hyperthyroidism, where the overactive thyroid produces too much hormone, which causes an individual to feel hot and flushed all the time, or its opposite condition of hypothyroidism, where an underactive thyroid produces too little hormone, leading to feelings of being cold. Medications are given to counter these (either to increase or decrease thyroid hormone production), but this is quite a fine balancing act; if a drug dose to treat hypothyroidism is too high, it can lead to overproduction of thyroid hormone, pushing a person into hyperthyroidism. It can then lead to common symptoms of an overactive thyroid, such as excessive sweating.⁸

Stimulants

Examples include:

• Amphetamines
• Methylphenidate (Ritalin)

These drugs, which are often used medically to treat disorders such as attention deficit hyperactivity disorder (ADHD) and narcolepsy, increase the amount of neurotransmitters noradrenaline and dopamine released into the synapse. It promotes a sympathetic response, which may lead to sweating, a feeling of overheating, or an accelerated heart rate, particularly during times of stress.⁹

Opioids and pain medications

Examples include:

• Morphine
• Codeine
• Buprenorphine

Opioid medications act as a depressant on the central nervous system. It can decrease the amount of neurotransmitter signalling and reduce the incidence of sweating. When the effects of the opioid wear off, a rebound effect can occur, resulting in excessive sweating. This is particularly noticeable if a person regularly takes a high dose of opioids and may be a sign of opioid withdrawal.¹⁰

Other medications

This is not a comprehensive list, and there are many other medications that can impact the way the body understands temperature, which can lead to abnormal sweating patterns. Before taking a new drug, always read the supplementary information provided in the medication pack.

How to manage medication-related sweating

It is important to recognise when your sweating becomes abnormal. Signs that this may be the case include:

• Excessive sweating, especially without a clear trigger like stress or physical activity
• Feeling hot, despite the temperature around you not being raised
• Heat exhaustion
• Feeling faint or dizzy

If these symptoms are starting to affect the quality of life, or are making you feel very unwell, then you should speak to the healthcare provider who can evaluate and adjust the dose of medications or even try you on a different kind of medication.

A healthcare provider can also exclude other crucial diagnoses that can cause excessive sweating by performing tests or evaluations, such as thyroid disease, phaeochromocytoma and even some cancers.

If medications are thought to be the primary cause, then doses can be adjusted or may be switched to an alternative preparation/medication to see if this helps.

Summary

Sweating or feeling excessively hot is a recognised side effect of several commonly prescribed medications. There are many potential reasons for this, and often it is necessary to change medication doses or preparations to find the right form. If one is concerned about these symptoms, it is important to discuss this with the healthcare provider, so that other underlying medical conditions can be investigated, and medications can be reviewed and changed if necessary.