COX inhibitor

A COX inhibitor is a drug that jams the enzyme cyclooxygenase, the production line that turns a fatty acid (arachidonic acid) into prostaglandins. Block the production line and the downstream products dry up: less pain-sensitising, fever-causing, inflammation-driving prostaglandin is made. Every NSAID is a COX inhibitor, and so is aspirin.

The twist is that cyclooxygenase comes in two main forms with different jobs. COX-1 is the always-on housekeeper, making prostaglandins that protect the stomach lining, support kidney blood flow, and help platelets clot. COX-2 is mostly switched on by injury and inflammation, making the prostaglandins that cause pain and swelling. Traditional NSAIDs block both, which is why they relieve inflammation but also damage the stomach.

This understanding led to selective COX-2 inhibitors (the coxibs, such as celecoxib), designed to relieve inflammation while sparing the protective COX-1 in the gut — and they do cause fewer ulcers. But because COX-2 also helps keep blood vessels healthy, selectively blocking it can shift the balance toward clotting and raise the risk of heart attack and stroke. One famous coxib was withdrawn for exactly this reason, a hard lesson that a cleaner-looking mechanism is not automatically a safer one.