From time immemorial humans have sought relief from pain and fever in various plant, animal, and mineral substances. By the 19th century, scientists were using chemical methods to isolate the pure active ingredients from these natural materials. Prompting this strategy were two drawbacks of natural remedies. First, the amount of active ingredients in the natural materials varied unpredictably, making it impossible to prepare and prescribe doses with predictable results. Second, because such materials contain many different chemicals, they often produced unwanted side effects. One early example of the new chemical strategy was the isolation of salicylic acid from the bark of the willow tree and its subsequent transformation into acetylsalicylic acid, or aspirin. Another popular pain reliever, Tylenol, also had its origins in 19th-century science, but the drug as we know it did not appear until 1955.
Within a two-week period in August 1897 the German chemist Felix Hoffmann synthesized two drugs: aspirin, one of the most widely beneficial drugs ever, and heroin, one of the most harmful of illegal substances.
Robert McNeil, Jr., a chemist and third-generation pharmacist, played a critical role in bringing Tylenol, the popular pain reliever and fever reducer, to market in the 1950s.