The history of aspirin an the medical use of it and related substances stretches back to antiquity, though pure aspirin (acetylsalicylic acid or ASA) has only been manufactured and marketed since 1899. Medicines made from willow and other salicylate-rich plants date back at least to 3000 BC, and were part of the pharmacopoeia of Western medicine in Classical antiquity and the Middle Ages. Willow bark extract became recognized for its specific effects on fever, pain and inflammation in the mid-eighteenth century. By the nineteenth century pharmacists were experimenting with and prescribing a variety of chemicals related to salicylic acid, the active component of willow extract.