Drug testing in the workplace: could a positive test for one of the mandated drugs be for reasons other than illicit use of the drug?

This manuscript reviews data available in the scientific literature relative to drug testing for the five mandated drug classes and circumstances other than abuse of the drug itself that could result in a positive test. For marijuana, passive inhalation, unknowing oral ingestion, and the use of Marinol are discussed. Data are presented on the concentration of delta9-tetrahydrocannabinol (THC) and its precursors, acid-A and acid-B, in illicit marijuana and the extent of extraction of THC in boiled (tea) or cooked products. For cocaine, passive inhalation and passive exposure issues are reviewed. For opiates, poppy seed ingestion and guidelines for exclusion of poppy seeds as a cause for a positive test are discussed. For amphetamines, issues such as the presence of other phenethylamines, l-methamphetamine (Vicks' inhalers), and other prescription drugs are discussed. Although passive inhalation of methamphetamine and phencyclidine is theoretically possible, no data were available on these issues.