How Does Medicine Bring Down Your Fever?

It’s 2 a.m., you’re sweating through the sheets, and every part of your body aches. You’ve got a fever, and you’re burning up from the inside out. So you fumble for a pill bottle, struggle a moment with the childproof cap,  and finally swallow an over-the-counter capsule. Maybe two. An hour later, you feel noticeably better. But what exactly happened? How can such a simple remedy convince your body to stop running hot?

The answer has to do with the fact that a fever isn’t your body overheating uncontrollably. It’s more like your internal thermostat is being deliberately turned up. Fever-reducing drugs such as aspirin, acetaminophen, and ibuprofen don’t cool you down directly, as if they were handy little chemical fans, but they do help reset your body’s thermostat. 

It’s a simple solution to a straightforward problem, but the way these medicines work is a different story — one whose ending still needs to be written.

The Heat Is Coming From Inside the House

Normally, your body works hard to maintain a relatively stable internal temperature that keeps you cool and comfortable. Deep in a brain region called the hypothalamus lies a kind of master thermostat that you can thank for achieving this homeostasis. It’s vital to systems that keep you alive, including your digestive and respiratory systems.

Think of your body as a computer or a car engine, which, if they run too hot, stop working correctly. They may even shut down completely. It’s important to keep your body temp stabilized to keep everything functioning properly.

This built-in defense mechanism creates a hostile environment for foreign viruses and bacteria — if an infection can’t take the heat, it needs to get out of the kitchen. Plus, higher temps help certain immune cells work more effectively.

That’s why fevers often begin with chills. As your temperature rises, you may shiver, pull on extra blankets, or feel cold. Your body is trying to reach the new target temperature dictated by that internal thermostat. Chills happen as your blood vessels constrict to conserve heat while your muscles contract to generate more of it, all in an effort to make you warmer.

Common fever reducers are used to interfere with that process. There are a few different kinds available over the counter, including acetaminophen (Tylenol) and non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs come in various types, including ibuprofen (Advil), naproxen (Aleve), and aspirin.

Scientists are still teasing out how some medicines work to bring down a fever. But it’s now thought that a hormone-like substance called prostaglandin E2 plays a key role. During an infection, levels of this organic compound rise, telling your master thermostat to get hotter. By reducing the effects of prostaglandin E2, certain drugs help guide the hypothalamus to lower your internal temperature back toward normal.

A fever isn’t really the enemy, since it’s meant to aid your immune system (though if the fever runs too high or lasts too long, that’s a different story). Once medicine turns down your thermostat, your body switches strategies. Blood vessels near the skin widen, allowing heat to escape, and sweating helps cool the body further.

So the next time your fever reducer of choice helps you get through a long, difficult night, remember that it isn’t acting like an internal air conditioner. Instead, it’s turning off the furnace, and allowing your body to return to its usual setting.