Bretazenil (Ro16-6028) is an imidazopyrrolobenzodiazepine anxiolytic drug which is derived from the benzodiazepine family, and was invented in 1988. It is most closely related in structure to the benzodiazepine antagonist flumazenil, although its effects are somewhat different. It is classed as a high-potency benzodiazepine due to its high affinity binding to benzodiazepine binding sites where it acts as a partial agonist. Its profile as a partial agonist and preclinical trial data suggests that it may have a reduced adverse effect profile. In particular bretazenil has been proposed to cause a less strong development of tolerance and withdrawal syndrome. Bretazenil differs from traditional 1,4 benzodiazepines by being a partial agonist and because it binds to alpha,1, 2, 3, 4, 5 and 6 subunit containing GABAA benzodiazepine receptor complexes. 1,4 benzodiazepines bind only to alpha 1, 2, 3 and 5 GABAA benzodiazepine receptor complexes.