Benzodiazepine is any of a group of mood-altering drugs, such as Librium and Valium, that are used primarily to treat severe anxiety or insomnia. These drugs, which intervene in the transmission of nerve signals (see nerve impulse) in the central nervous system, were originally developed as muscle relaxants. Today they are widely prescribed as tranquilizers. Benzodiazepines may produce a number of side-effects, including drowsiness, unsteadiness, and confusion. Also, they are known to cause dependence. For these reasons, they are recommended only for short-term use.