False positive urine drug screens from quinine in tonic water.

Urine surveillance of patients is a universal procedure in drug treatment programs for monitoring frequency and type of illicit drug use. The method is also being increasingly utilized by employers to screen employees for drug use. The presence of a prescribed substance in a subject's urine is considered objective evidence of illicit drug use, and is used to confront subjects. However, studies have demonstrated that urine surveillance is not infallible. The presence of inaccuracy in urine surveillance has definite negative consequences of both individuals and the testers. In this paper, we report that a positive urine test for quinine, which may be evidence of illicit drug use, results from the consumption of the amount of tonic water present in a mixed drink. The implications of this finding are discussed.