Drug interactions in controlled clinical trials.

As much information as possible should be obtained in clinical trials to assess possible interactions between test drugs and concomitant medications prescribed for other medical indications. Side effect profiles were compared in patients taking buspirone, mean = 20 mg/day; diazepam, 20 mg/day; clorazepate, 23 mg/day; and placebo, with or without concomitant medications. Approximately 1,000 anxious patients were included in the analysis; 700 received buspirone. The use of a variety of common medications did not affect the side effect profile in the buspirone, clorazepate, and placebo groups, but did increase the incidence of side effects in the diazepam group. The increased incidence of sedation noted with diazepam and clorazepate, however, was not due to concomitant medication.