A milestone in the history of the medications commonly known as tranquilizers occurred in the early 1960s, when the first benzodiazepines arrived on the market. This new class of medications soon supplanted barbiturates, a powerful class of sedatives that were
commonly used at the time and that act on the brain's GABA receptors.
The reason for this rapid success was that benzodiazepines were soon found to have a lower risk-to-benefit ratio than barbiturates. Benzodiazepines are at least as effective as barbiturates, have the same or fewer side effects, and have a far lower acute toxity (an overdose of barbiturates can even result in death).
One caveat, however: as far as dependency is concerned, benzodiazepines are no better than barbiturates. People who use benzodiazepines for a long time must undergo a difficult withdrawal process.