A chemical substance is used to reduce tension and anxiety and induce calm (sedative effects) or induce sleep (hypnotic effects). Most sedative-hypnotic drugs exert a quieting or calming effect at low doses and a sleep-inducing effect in larger doses. They tend to depress the central nervous system and can be obtained with other drugs, such as opiates. They achieve their effects without affecting mood or reducing sensitivity to pain.
For centuries alcohol and opium were the only drugs that had sedative-hypnotic effects. Chloral hydrate, a derivative of ethyl alcohol, was introduced in 1869. Paraldehyde was introduced into clinical medicine in the 1880s, followed by the synthesis of barbital in 1903. Phenobarbital became available in 1912 and was followed by a long series of barbiturates. In the mid-20th century, new types of sedative and hypnotic drugs were synthesized.
Barbiturates were extensively used as “sleeping pills” throughout the first half of the 20th century. They were also used to reduce voluntary inhibition during psychiatric examinations. When taken in high doses, they produce a deep unconsciousness. In still higher doses they depress the central nervous and respiratory systems to the point of coma, respiratory failure, and death.
The prolonged use of barbiturates for the relief of insomnia leads to tolerance and addiction. Some of these drugs can also cause sleep disruption, as shown by electroencephalographic (EEG) patterns during barbiturate-induced sleep. The use of some of them can cause convulsions.
The use of barbiturates declined after the development of benzodiazepines in the 1950s. The latter is more effective in relieving anxiety than inducing sleep, but they are superior to barbits because of the reduced dangers of tolerance and addiction. They require a much smaller dosage to achieve their effects.