Central nervous system depressants, e.g. alcohol, barbiturates, and benzodiazepines, have a wide spectrum of activity in human and animals. These depressants produce varying degrees of CNS depression，depending mainly upon the dose used. In small does，they can alleviate anxiety and/or reduce spontaneous activity; in moderate doses, they induce sleep; with large doses, severe CNS depression progresses to anesthesia, coma or even death. This graded, dose-dependent CNS depression is a conunon feature of these agents. In addition to causing CNS depression, these agents also possess other pharmacological properties, e. g. muscle relaxation, anticonvulsant activity, respiratory depression, hypothermia, etc.