Benzodiazepines, often abbreviated to "benzos", are a class of psychoactive drugs with varying hypnotic, sedative, anxiolytic (anti-anxiety), anticonvulsant, muscle relaxant and amnesic properties, which are mediated by slowing down the central nervous system. Benzodiazepines are useful in treating anxiety, insomnia, agitation, seizures, and muscle spasms, as well as alcohol withdrawal. They can also be used before certain medical procedures such as endoscopies or dental work where tension and anxiety are present, and prior to some unpleasant medical procedures in order to induce sedation and amnesia for the procedure. Benzodiazepines are also used to treat the panic that can be caused by hallucinogen intoxication. Benzodiazepines can cause a physical dependence and addiction. Upon cessation of long term use a benzodiazepine withdrawal syndrome can occur. Combination of these drugs with alcohol or opiates is particularly dangerous, and can lead to coma or death. The various benzodiazepines differ in their toxicity since they produce varying levels of sedation in overdose, with oxazepam being least toxic and least sedative and temazepam being most toxic and most sedative in overdose.