Barbiturates are a class of drugs acting on the central nervous system which may be used as sedatives, anesthetics, or anticonvulsants. They depress nerve cell activity, the degree of depression and thus clinical effect varying in different members of the class. Although widely used in the past for insomnia, the use of barbiturates is now discouraged because of high rates of addiction and their danger in over-dosage; safer alternatives are now available. Short-acting barbiturates are used in anesthesia; phenobarbitone is used in treatment of convulsions, often in combination with other drugs.