The document discusses several classes of sedative-hypnotic drugs including benzodiazepines, barbiturates, and other nonbarbiturate sedative-hypnotics. Benzodiazepines act by enhancing the effects of the inhibitory neurotransmitter GABA at GABA-A receptors and have a wide margin of safety. Barbiturates also enhance GABA effects but are no longer recommended due to their narrow therapeutic range and potential for abuse and dependence. Chloral hydrate is a relatively safe nonbarbiturate hypnotic used in some patient populations.