NSAID

When tissue is injured, the body sends out chemical alarm messengers that cause pain, swelling, and fever. NSAIDs work by switching off the factory that makes those messengers, so the alarm quiets down. That is why one pill can ease a headache, a sprain, and a fever at once.

The factory is the cyclooxygenase enzyme (COX), which converts arachidonic acid into prostaglandins, the local hormones behind inflammation, pain, and fever. NSAIDs inhibit COX, usually by reversibly blocking its active-site channel; most are weak carboxylic acids whose negative charge helps anchor them where arachidonic acid would sit.

There are two relevant forms: COX-1, which helps protect the stomach lining and support platelets, and COX-2, which is induced at sites of inflammation. Traditional NSAIDs such as ibuprofen and naproxen block both, while 'coxibs' such as celecoxib were designed to spare COX-1 and reduce stomach injury.

An honest caveat: blocking COX-1 can irritate the stomach and cause ulcers or bleeding, while heavy COX-2 selectivity has been linked to cardiovascular risk, so NSAID choice and dose are a careful balance. Note that aspirin is a special case, irreversibly modifying COX rather than just sitting in it.