Actual versus reported benzodiazepine usage by medical outpatients.

Benzodiazepines are widely prescribed, and in 1979 almost 10% of the adult population was taking them. Prior studies of outpatient usage of benzodiazepines have relied on survey or prescription data, which may be confounded by noncompliance. To determine the actual use of benzodiazepines, plasma benzodiazepine concentrations were measured in 225 consecutive outpatients from a university cardiology outpatient service. Self reports indicated that the great majority of the patients (191) were taking at least one medicine, and 70 reported being on a psychotropic drug. Seventy-seven patients reported taking benzodiazepines, the majority being on bromazepam (20), diazepam (26) or oxazepam (19). In 25 of those 77 patients, the reported drug could not be detected in plasma. Conversely, in 10 of the 225 patients, benzodiazepines which were not reported were detected (diazepam or flurazepam). Of those taking benzodiazepines, many had a low concentration, suggesting intermittent rather than regular use. Thus, many patients for whom benzodiazepines are prescribed take them irregularly, and a small group uses them without reporting their prescription. These findings have implications for the clinical presentation of illness and for the possibility of drug interactions.