Nonsteroidal anti-inflammatory drugs (NSAIDs)

Nonsteroidal anti-inflammatory drugs, or NSAIDs, are medicines that bring down fever (which is why they're called antipyretics), ease pain (analgesics), and calm inflammation (anti-inflammatories). The “nonsteroidal” part of the name just means they don't belong to the steroid family. What's interesting is that they do all of this mainly in one way: by blocking an enzyme called cyclooxygenase, or COX. An enzyme is a protein the body uses as a tool to turn one molecule into another.

Think of COX as a machine in a factory. A raw material called arachidonic acid goes in one end, and finished molecules come out the other: prostaglandins, thromboxanes, and prostacyclins. An NSAID puts the brakes on that machine. What the medicine does against fever, pain, and inflammation is attributed to exactly that: those molecules go missing.

But the factory doesn't have just one machine. It has two versions of it, called isoenzymes. COX-1 is installed all the time, and it helps keep the gastrointestinal mucosa in good shape. That's the lining that covers the inside of your stomach and intestines. It also helps maintain kidney function, meaning the work your kidneys do. COX-2, on the other hand, is the one that gets installed when there's inflammation. Most NSAIDs slow down both machines, COX-1 included, and the stomach damage they can cause probably comes from putting the brakes on COX-1.