Aspirin

Aspirin, also known by its chemical name acetylsalicylic acid (ASA), is a medication that functions by irreversibly inhibiting cyclooxygenase (COX) enzymes, specifically COX-1 and COX-2. These enzymes are crucial for the synthesis of prostaglandins, hormone-like substances that mediate pain, inflammation, and fever. By blocking prostaglandin production, aspirin effectively alleviates these common symptoms. Its therapeutic effects are dose-dependent. At standard doses, it acts as an analgesic for mild-to-moderate pain (such as headaches and muscle aches), an antipyretic to reduce fever, and an anti-inflammatory for conditions like arthritis.

A distinct and critical function of aspirin occurs at low doses (typically 75-100 mg daily), where it serves as an antiplatelet agent. It permanently blocks the production of thromboxane A2 in platelets, a substance that causes them to aggregate and form blood clots. Because platelets lack a nucleus and cannot synthesize new enzymes, this effect lasts for their entire lifespan (about 7–10 days). This property is fundamental to its role in preventing cardiovascular events, such as heart attacks and ischemic strokes, in high-risk individuals. However, this same mechanism increases the risk of bleeding, most commonly in the gastrointestinal tract. It is also contraindicated in children and teenagers with viral infections due to the risk of Reye's syndrome, a rare but serious condition causing swelling in the liver and brain.

Aspirin is one of the first and most widely known members of the nonsteroidal anti-inflammatory drug (NSAID) class, which also includes ibuprofen and naproxen. While all NSAIDs inhibit COX enzymes, aspirin's irreversible inhibition of COX-1 is unique and underpins its potent antiplatelet effects. The history of aspirin dates back to antiquity, with remedies derived from willow bark, which contains the related compound salicin, being used to treat fever and pain. The active metabolite, salicylic acid, was isolated in the 19th century, but it was harsh on the stomach. In 1897, chemist Felix Hoffmann at the German company Bayer synthesized a more tolerable form, acetylsalicylic acid, which was marketed as Aspirin and became one of the first mass-produced synthetic drugs.