This term has now been superseded by hypnotics and anxiolytics. A tranquillizer is principally a drug that takes away anxiety and is now synonymous with anxiolytics.
These drugs can be divided into the benzodiazepines and barbiturates. The latter are very rarely used nowadays because of their side effects and rapid addictive qualities. The former are less addictive – but only just. Diazepam is the most common drug indicated for the short-term relief of severe anxiety. The benzodiazepines can be long- or short-acting drugs but are being replaced by sustained serotonin re-uptake inhib-iters , principally Prozac.