Background noise in healthy volunteers--a consideration in adverse drug reaction studies.

In adverse drug reaction studies proper control over 'Back ground noise' is to be maintained to avoid erroneous conclusions to be drawn for adverse drug effects. Healthy volunteers, not taking any medication, were surveyed by a questionnaire to obtain data on the occurrence of any symptoms, often ascribed to side effects of drugs. Only 62 subjects out of a total of 236 (26.27%) stated experiencing none of these symptoms during the previous 3 days. The remaining subjects reported some symptoms, with an median number of symptoms experienced per person being 2; the most common being fatigue; headache, inability to concentrate and excessive sleepiness.