Benzodiazepines were first marketed in the 1960s. It has only been recently that an awareness has developed that benzodiazepines share many of the undesirable side effects of the barbiturates. A number of toxic CNS effects are seen with chronic high dose benzodiazepine therapy. These include headache, irritability, confusion, memory impairment, depression, insomnia and tremor. The risk of developing over-sedation, dizziness and confusion increases substantially wit higher doses of benzodiazepines.
Prolonged use can lead to physical dependence even at recommended dosages.
Unlike barbiturates, large doses of benzodiazepines are rarely fatal unless combined with other drugs or alcohol. Although primary abuse of benzodiazepines is well documented, abuse of these drugs usually occurs as part of a pattern of multiple drug abuse. At therapeutic doses, chloral hydrate has little effect on respiration and blood pressure but, a toxic dose produces severe respiratory depression and very low blood pressure. Although chloral hydrate is still encountered today, its use declined with the introduction of the barbiturates. More than 2,500 barbiturates have been synthesized, and in the height of their popularity about 50 were marketed for human use.