korien_oct13_wikimediacommonsPeople had known for a long time that willow tree bark had an ability to relieve pain. Modern aspirin was developed in the 19th century. The word “aspirin” started as a brand name of the company Bayer, but became a generic name for the drug. Aspirin is less popular since the invention of other pain killers in the middle of the 20th century. It’s also poisonous to many pets!