"It is well known that the intravenous infusion of benzodiazepines, such as Valium or Ativan, typically produces a similar amnesia for the several hours surrounding the infusion. While this may be a benefit in forgetting the painful effects of surgery, it becomes a potentially serious problem in the routine use of the minor tranquilizers for anxiety or sleep disorders and can interfere with psychotherapy, studying, learning anything new, or recalling previously retained memories."

From: http://www.breggin.com/minortranqs.html