The anti-inflammatory properties of the extract of willow bark have been known for centuries. Salicylic acid was discovered as the extract's active ingredient in the nineteenth century and was subsequently acetylated to improve its gastrointestinal tolerability; acetylsalicylic acid became the prototypical analgesic aspirin. Aspirin and other related compounds constitute a class of drugs known as NSAIDs. All NSAIDs have three desirable pharmacological effects—anti-inflammatory, analgesic, and antipyretic. NSAIDs and acetaminophen are among the most commonly prescribed medications for acute and chronic pain and can also be obtained without a prescription.