What enzyme does aspirin inhibit?

The enzyme inhibited by aspirin is cyclooxygenase, commonly abbreviated COX.

Aspirin irreversibly acetylates cyclooxygenase enzymes, especially COX-1 and, at different sites and effects, COX-2. These enzymes normally help convert arachidonic acid into prostaglandins and thromboxanes. Prostaglandins contribute to pain, inflammation, and fever, while thromboxane A2 promotes platelet aggregation. Blocking their production explains aspirin’s pain-relieving, fever-reducing, anti-inflammatory, and antiplatelet effects.

Aspirin’s lasting action on platelets is particularly important. Platelets cannot readily manufacture replacement cyclooxygenase, so the effect can persist for much of the platelet’s lifespan, roughly 7 to 10 days. This is why low-dose aspirin has been used in selected cardiovascular settings, although it can also increase bleeding risk and is not appropriate for everyone.

The mechanism was clarified by British pharmacologist John Robert Vane, whose 1971 work linked aspirin and related drugs to reduced prostaglandin production. He shared the 1982 Nobel Prize in Physiology or Medicine for discoveries concerning prostaglandins. Aspirin differs from many other NSAIDs because its inhibition of COX is irreversible; drugs such as ibuprofen generally inhibit the enzyme reversibly.