Sedative-hypnotics are central nervous system depressants used typically to bring on sleep or to sedate during the daytime. These drugs all induce a broad and non-specific depression of physiological functions because the CNS is so responsive to their depressant effect. This makes them especially useful because they induce sedation without depressing any other bodily functions.

However, this beneficial sleep-inducing effect typically wears off within two to three weeks of use because the CNS develops a tolerance to the sedative effect of the psychoactive chemicals. Because of this, many doctors rarely prescribe CNS depressants unless they are for a short period of therapy. The effects of CNS depressants on an individual's physical and mental state are tolerance (as such chiefly used only for brief therapy), withdrawal, potentiation (when coupled with other depressants), reduced inhibition, hostility, agitation, depression, brain damage with long-term use, and habituation.

Pharmacologically, effects are anti-anxiety, anti-seizure, depressed respiration, disinhibition, euphoria, incoordination, mood swings, and sedation. Withdrawal effects from CNS depressants are restlessness, anxiety, seizures, toxic psychosis (such as DTs or death), normal or impaired inhibition, dysphoria, normal or impaired coordination, excitation, tremors, and sweating.

Other adverse effects that result from sedative use are potentiation of a sedative's respiratory depressant effects coupled with alcohol use, mental depression when used chronically, habituation (such as when a person is so used to taking two pills to sleep at night that he/or she mentally cannot sleep without them), and anger.