Common Herbal Supplements Did Not Produce False-Positive Results on Urine Drug Screens Analyzed by Enzyme Immunoassay To the Editor:

The use of the urine drug screen (UDS) to test for substances of abuse has become commonplace b cause urine is relatively easily obtained and concentrations of drug in urine tend to be higher than in other biological matrices (1). The UDS is increasingly utilized as a pre-employment requirement, toxicological screen in the emergency room, as part of a general admissions medical screen at inpatient psychiatric facilities, and as a measure of abstinence in patients being treated at substance abuse facilities (2). Also, members ofthe armed services and athletes are subject to periodic or random screens. Additionally, "off site " diagnostic kits are increasingly being utilized. Positive results are highly suggestive that an individual has been using the substance inquestion. The major UDS test methods used in the U.S. are automated immunoassay tests uch as radioimmunoassay (RIA), fluorescence polarization immunoassay (FPIA), and enzyme immunoassay (EIA) (2). It has been recognized that a number of medications (2,3), certain foods (4), and herbal products (5) may cross-react and/or produce "false-positive " results for a number of analytes. The use of herbal supplements has expanded dramatically in the last decade and as part of our ongoing herb-drug interaction studies we sought to determine their potential to confound the results of the UDS. Accordingly, we assessed normal volunteers participating in a series of studies for the potential of commonly utilized herbal preparations to produce "false positive " results during formal study