sedative-hypnotic
A sedative-hypnotic is a drug that turns the brain's volume down. In smaller doses it takes the edge off, leaving you calm and relaxed (the sedative effect); in larger doses it tips you over into sleep (the hypnotic effect). The two effects are not really different actions but points on a single dose-dependent slope of central nervous system depression.
Most clinically used sedative-hypnotics work by enhancing the inhibitory neurotransmitter GABA, making neurons harder to fire. The major families are the benzodiazepines, the older barbiturates, and the newer non-benzodiazepine 'Z-drugs' such as zolpidem. They are prescribed for insomnia, acute anxiety, agitation, and as adjuncts in anaesthesia and seizure control.
The same mechanism that calms the brain can dangerously slow it. As the dose climbs, sedation can deepen into stupor, coma, and respiratory depression, especially when combined with other CNS depressants like opioids or alcohol. Long-term use also breeds tolerance and physical dependence, so these drugs are best used at the lowest effective dose for the shortest necessary time.
A patient with short-term insomnia after surgery is given a low dose of zolpidem at bedtime for a few nights, then weaned off to avoid dependence.
Sedative-hypnotics are most appropriate for brief, defined episodes rather than chronic use.
Benzodiazepines and Z-drugs have a wider margin of safety than barbiturates because their GABA enhancement has a ceiling, so a pure overdose is less likely to be fatal — but combining them with alcohol or opioids removes that safety and can stop breathing.