Benzodiazepines and Z-drugs have pharmacodynamic effects with tolerance that can occur quickly, after one week to one month of treatment and that concerns hypnotic and anxiolytic properties in particular. Old studies showed a real but poor short-term efficacy of benzodiazepines on anxiety and sleep disturbances. Long-term efficacy of benzodiazepines can be confused with the occurrence of rebound effect, discontinuation symptoms or relapse when the treatment is quitted; they contribute to an apparent efficacy, as well as the symptoms removal when treatment is re-initiated. Pharmacologic tolerance exists with respects to efficacy and side effects that decrease over time, in the first weeks of treatment. Its main associated characteristic is the occurrence of a severe withdrawal syndrome when treatment is quitted. To limit long-term treatments, it is relevant to target treatment initiation of benzodiazepines and to restrict indications and treatment duration. Addiction to benzodiazepines is frequent in patients treated for another addiction; it is associated with more frequent complications, in particular overdoses and suicide attempts. The use of benzodiazepines is necessary to prevent complications during alcohol or benzodiazepine withdrawal, but duration of treatment should be limited and dispensing should be supervised in patients with substance use disorders.< Leer menos