Benzodiazepines were first synthesized in the 1930s but were not systematically evaluated until 20 years later. The introduction of chlorpromazine and meprobamate, which had sedative effects in animals, in the early 1950s, led to the decade of development of sophisticated in vivo pharmacological screening methods that were used to identify the sedative properties of benzodiazepines. More than 3,000 benzodiazepines have been synthesized since chlordiazepoxide, which was synthesized by Sterbach in 1957, was introduced into clinical medicine. About 40 of them are in clinical use.