How Stimulants Turn Off Your Body's Heat Alarm

Stimulants don't just let an athlete's body run hotter in the heat. They can also quiet the warning signals that would normally make that athlete slow down.

I've written before about how ADHD stimulants can raise core temperature in athletes. In this post, I want to explain how. To understand it, you first need to know about a safety system built into your brain.

Your brain's heat brake

When you exercise in the heat, your core temperature climbs. As it gets close to about 104°F (40°C), your brain steps in. It turns down the signal to your muscles, so you slow down, feel exhausted, and want to stop.

Your muscles can still work at that point. It's your brain pulling back. Researchers call this central fatigue, and you can think of it as your brain's built-in heat brake.

Two classic studies from Copenhagen showed how consistent this brake is:

• Fatigue happens at the same temperature. Trained cyclists exercising in 104°F heat started at different body temperatures and heated up at different rates. They still reached exhaustion at almost exactly the same core temperature, about 40.1 to 40.2°C (104.2 to 104.4°F) (González-Alonso et al., 1999).
• The brain, not the muscle, is what gives out. When cyclists were overheated to about 40°C, they couldn't hold a maximal muscle contraction as well as when their core temperature was normal. The drop came from reduced drive from the brain to the muscle (Nybo & Nielsen, 2001).

Some researchers think the brain also anticipates overheating and starts easing off the muscles before core temperature gets that high. Either way, the point is the same: the brain is protecting you.

How stimulants interfere with the brake

Stimulants can interfere with that brake in three ways. The first is the best supported. The third is the least.

1. The brake gets overridden

The heat brake is tied closely to dopamine, the brain chemical that drives motivation and the urge to keep going. One leading theory is that fatigue sets in when the balance of brain chemicals shifts away from dopamine, and that this matters most in the heat.

Stimulants like Adderall and Ritalin keep dopamine high. When researchers boosted dopamine in athletes exercising in warm conditions, fatigue was delayed. Boosting it in cool conditions didn't change much (Roelands et al., 2015).

So the brain keeps telling the muscles to go. And that matters, because working muscles turn most of the energy they use into heat, not movement. The athlete keeps pushing and keeps producing heat, past the point where they'd normally slow down.

2. The alarm goes quiet

The clearest evidence comes from a study of trained cyclists (Roelands et al., 2008). Eight men took a single 20 mg dose of Ritalin (methylphenidate) or a placebo, then rode a time trial in either cool (64°F) or warm (86°F) conditions.

• In the cool room, Ritalin made no difference.
• In the heat, they finished about 16% faster on Ritalin. Their core temperatures climbed above 40°C (104°F).
• They didn't feel it. On Ritalin, the riders rated the effort and the heat the same as on placebo.

Their bodies were overheating, and their brains weren't sounding the alarm. A similar study with bupropion (Wellbutrin), which also raises dopamine, found the same pattern: faster in the heat, hotter at the end, with no change in how hard or how hot it felt (Watson et al., 2005).

3. Heat may get trapped

This one is more theory than proof, so I want to be clear about what we know.

Stimulants turn on your "fight or flight" system. That system can nudge the brain's thermostat, the hypothalamus, and tighten blood vessels in the skin. Your skin is one of the main ways you release heat, so less blood flow there could mean more heat stays inside.

That effect has been shown clearly with other stimulant drugs in animals. It hasn't been tested in athletes taking ADHD medication at normal doses. In the bupropion cyclist study, skin temperature actually ran higher, which doesn't look like the skin shutting down.

There's also fuel and fluid. Stimulants commonly dull appetite, and an athlete who skips a meal also misses the water and salt that come with it. Whether stimulants make athletes drink less is less clear. Some researchers think they may actually increase thirst.

This is about awareness; not stopping meds.

So stimulants don't just turn up the heat. They can turn down the alarm. But that doesn't mean medication is the problem.

A large 2024 study looked at medical records from about 139,000 young people with ADHD, ages 6 to 24 (Zinabu et al., 2024). Over one year, those prescribed stimulants were about 44% less likely to have a heat-related illness than those who weren't.

The authors offered a few possible reasons. Better-managed ADHD may mean better planning, less impulsive behavior, and better self-care, including drinking and resting when you should.

A few important limits:

• Most of the difference was dehydration. There was no clear difference in heat exhaustion or heat stroke, and some dehydration diagnoses may not have been heat-related at all.
• It only counted people who saw a doctor. Milder cases weren't captured.
• It wasn't a study of athletes. It didn't track exercise, weather, or whether people took their medication that day.

So this isn't about stopping medication. It's about knowing the alarm may be quieter during hard exercise in the heat.

What athletes and parents can do

These matter most on hot and humid days, during double sessions, and in long tournaments.

1. Schedule breaks. Build rest and cooling breaks into practice ahead of time, rather than waiting for the athlete to ask for one.
2. Have a hydration plan. Drink on a schedule, not by thirst. Make sure your athlete eats before training, even if their appetite is low.
3. Don't trust "I feel fine." On a stimulant, feeling OK may not mean the body is OK. Coaches and parents should watch for warning signs like dizziness, confusion, unusual clumsiness, or a sudden drop in performance.
4. Talk to the prescriber about timing. Ask about game-day and practice-day timing, especially for hot-weather competition. Don't change the dose or stop on your own.

This post is for educational purposes only and is not medical advice. Talk with your physician before starting, stopping, or changing any medication.

References

1. González-Alonso J, et al. Influence of body temperature on the development of fatigue during prolonged exercise in the heat. J Appl Physiol. 1999;86(3):1032–1039.
2. Nybo L, Nielsen B. Hyperthermia and central fatigue during prolonged exercise in humans. J Appl Physiol. 2001;91(3):1055–1060.
3. Roelands B, De Pauw K, Meeusen R. Neurophysiological effects of exercise in the heat. Scand J Med Sci Sports. 2015;25(Suppl 1).
4. Roelands B, et al. The effects of acute dopamine reuptake inhibition on performance. Med Sci Sports Exerc. 2008;40(5):879–885.
5. Watson P, et al. Acute dopamine/noradrenaline reuptake inhibition enhances human exercise performance in warm, but not temperate conditions. J Physiol. 2005;565(Pt 3):873–883.
6. Zinabu S, et al. Stimulant medications effects in heat-related illness in ADHD patients: a large database study. Front Psychiatry. 2024;15:1509385.