Benzodiazepines (BZD), sometimes called "benzos", are a class of psychoactive drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. The first such drug, chlordiazepoxide (Librium), was discovered accidentally by Leo Sternbach in 1955, and made available in 1960 by Hoffmann–La Roche - which, since 1963, has also marketed the benzodiazepine diazepam (Valium). In 1977 benzodiazepines were globally the most prescribed medications.