How certain medications impact heat sensitivity and sun sensitivity and how you can survive a hot summer

Being prescribed dexamphetamine to treat her ADHD has been a massive change for the better for Linly Karshagen — but how it changed her relationship with heat was unexpected.

The 23-year-old was diagnosed with attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) last year.

Like with many others, general awareness of the two conditions helped her realise she was neurodiverse, along with her work as an occupational therapist among other neurodiverse people.

But in 35-degree days in her Brisbane home with a broken air-conditioner, her tolerance and sensitivity to heat have become front of mind.

“We’re prone to sensory overwhelm a lot earlier than most neurotypical people are, and we can have trouble processing sensory information,” Ms Karshagen said.

“So yeah, definitely [the heat] does kind of creep up on you and then all of a sudden it’s too hot and probably then you get quite irritable.”

A growing number of Australian adults are being diagnosed with ADHD and prescribed medication to help manage it.

However, a side effect common among different ADHD medications is heat sensitivity.

As more and more people receive these diagnoses and are prescribed medication, the number of Australians potentially at higher risk during the long, hot and dry summer also increases.

Tara, 22, is one of many of those Australians who recently realised they were neurodiverse thanks to information being shared on TikTok along with befriending other neurodiverse people.

“We tend to flock together. I noticed that my behaviours are a lot similar to theirs and was thinking ‘Ohh, is that normal? I thought everyone did that a lot with their behaviours,'” they said.

She saw her doctor and was prescribed dexamphetamines but felt the adverse side effect on a family day at a theme park that abruptly ended when she felt the sudden onset of heat stroke.

Even after returning to her hotel and sitting in the aircon, symptoms of nausea and dehydration took hours to go away.

“I was just like, why do I feel so nauseous? Why am I still sweating when the aircon’s been on all day? I need water but I feel sick, like too sick to drink any,” she said.

Why do these medications have this effect?

Medications used to treat ADHD, depression and other psychiatric conditions all share heat sensitivity as a common side effect, according to Jarrod McMaugh, the Pharmaceutical Society of Australia’s Victorian state manager.

Mr McMaugh says these medications work by increasing the activity of dopamine, serotonin and noradrenaline in some parts of the brain.

“It’s really important to understand that those neurotransmitters are all over the brain,” he says.

“They do a whole range of different functions, [including] in the areas of the brain that regulate heat action and body heat regulation.

“If you get an increase or decrease in those things, then sometimes it affects your ability to detect how hot you are.

“So the primary issue with heat regulation with these medications is that it’s not that it makes you more likely to become overheated, it’s more a matter of how you notice how the heat is affecting you.”

This also means the brain can fail to detect when you are dehydrated, a potentially concerning combination of side effects.

Just taking this type of medication, Mr McMaugh says, does not mean you are likely to overheat in a situation where overheating is not already likely.

“It’s more a matter of, are you exposing yourself to high levels of heat?” he says.

Exposing yourself to direct sunlight for a prolonged period or napping in a hot car are good examples of this.

His advice is to make sure you’re taking the usual steps you would take to avoid heat stroke, such as seeking shade and drinking plenty of water.

Heat intolerance

Another heat-related side effect common to these types of medication is heat intolerance, Dr Jessica Pace from the University of New South Wales School of Pharmacy said.

“These ADHD and antipsychotic medicines raise your temperature by acting on the hypothalamus, the region of the brain essential for cooling,” she said.

“The drug levothyroxine, used to treat an under-active thyroid, also increases your body temperature, this time by increasing your metabolism.

“Other medicines constrict [tighten] blood vessels, decreasing blood flow to the skin, and so prevent heat from escaping this way. This means your body can’t regulate its temperature as well in the heat.”

These medications can include beta-blockers, medication for high blood pressure, angina, decongestants and some migraine medication.

Dr Pace says not every person who uses these prescribed drugs necessarily has a reaction.

“If it does happen, it can be a one-time occurrence or it can happen each time the drug is taken. These side effects are relatively rare. The exact percentage of people affected varies depending on the medication but it is usually less than 1 per cent of the people who use it.”

Dr Pace says it can also be helpful to establish a practice of check-ins with friends and neighbours, particularly including older or other vulnerable people.

Research gaps

A study published in the British Journal of Pharmacology in 2021 repeats what Mr McMaugh says, noting adverse effects from stimulants are usually from recreational use.

However, Dr Pace says research around prescription medication and heat remains minimal.

“A variety of studies show that people taking certain classes of medications are more likely to need emergency care and that there is a link between certain medications and a higher chance of death during extreme heat events,” she said.

“Anecdotally, clinicians also see more people who take the medicines discussed here in hospitals suffering from heat illness.

“However, overall, more research is needed to make direct connections between specific prescription medications and the exact contribution to heat illness — and to understand whether the risks to people on multiple medicines are even higher.”

Sunburn risk

As temperatures keep climbing throughout the summer, there are other medication side effects you need to watch out for.

Medications for acne, certain heart problems — like arrhythmia — and some antibiotics all increase the risk of sunburn — known as sun sensitivity or photosensitivity.

This is because of the way skin cells generate as they come closer to the surface, according to Mr McMaugh.

Usually, he says, skin cells dry and flatten out as they reach the skin’s surface, making the dead skin cells work as a barrier against the sun.

“These medicines that we’re talking about may slow that process down,” he says.

“So by the time their skin cells reach the surface, they’re not flat-out dry and dead the way they normally would be.”

Commonly, these types of medication will see people start to burn who usually wouldn’t – they’ll also tend to burn faster, increasing the severity and the recovery time.

Dr Pace said there were two main ways that medications could increase your risk of sunburn: a phototoxic reaction and a photoallergic reaction.

“A phototoxic reaction is the most common way for a medication to cause an increase in sun sensitivity,” she said.

“This is where the drug molecule is able to absorb UV light and then releases it back into the skin. Once the oral medication has been absorbed into the bloodstream, or after the topical medication is applied to the skin, a phototoxic reaction can occur anytime within minutes or hours of sun exposure.

“Typically, only the skin that is exposed to the sun will react.”

She said the less common second reaction, photoallergic, happens when after being exposed to the sun, the drug undergoes structural changes.

“Once these structural changes happen, small proteins in our body can bind to the drug, resulting in our immune system recognising it as a foreign substance. Then antibodies are produced to fight it,” she said.

The result can be similar to eczema or a red rash and can take anywhere between one to three days to occur.