Practical Challenges to Positive Drug Tests for Marijuana

With the advent of drug testing in the workplace and the consequences of a positive drug test, several issues have arisen in defending or explaining a positive result for a given drug of abuse. Marijuana is the illicit drug with the highest percentage of positives in workplace drug testing. Consequently, marijuana was the first such drug for which excuses were provided to explain the positive test result.Passive inhalation was the first defense offered. This prompted several studies to ascertain whether passive inhalation of marijuana smoke could produce a positive drug test (1)(2)(3)(4). The majority of these studies showed that although passive inhalation of marijuana smoke under certain circumstances could produce detectable concentrations of Δ-9-tetrahydrocannabinol (THC) metabolite in urine, those concentrations were not above the cutoffs used under the federal workplace drug testing guidelines (50 μg/L for screening and 15 μg/L for confirmation). One study (5), however, showed that concentrations above these cutoffs could be attained when the exposure conditions were very severe and, hence, unrealistic. Today, passive inhalation is not nearly the issue that it was at the beginning of drug testing in the workplace.The second issue was passive ingestion. Unknowing ingestion of marijuana tea, brownies prepared with marijuana, or the like was the line of defense that followed passive inhalation. Although studies were carried out to investigate this issue (6)(7), there was no question that if someone orally ingested cooked marijuana, urinary excretion of Δ-9-THC …