The passive exposure to marijuana smoke is often proposed as a reason for a positive drug test?

(Excerpt reprinted with permission, by Michael A. Peat, PhD, DABFT and Judy J. Peat)

Marijuana is commonly smoked in social situations where not all who are present smoke the drug. The passive exposure to marijuana smoke is often proposed as a reason for a positive drug test. However, numerous studies have examined this possibility and have shown that under normal conditions passive inhalation will not cause positive results. Only under extreme conditions will the urine concentrations by immunoassay and GC/MS exceed the cutoffs commonly used. A study of passive inhalation under extreme conditions was reported by Cone et al. Some participants found the amount of smoke sufficient to require wearing of eye goggles. During the exposure, the volunteers felt both the psychological and physiological effects of THC.

A more realistic study was conducted by Law and coworkers. In this study, six volunteers each smoked one marijuana cigarette (6 total) in a small room (27,950 L). They smoked the cigarettes in their normal manner, taking between 10 and 34 minutes to finish all cigarettes. The smoking volunteers left the room when their marijuana cigarettes were finished. Four nonsmoking volunteers were in the room for the entire smoking period and remained within the room for three hours from the time the smoking began. These subjects provided specimens at 1, 2, 3, and 6 hours from the beginning of smoking. Specimens were analyzed for carboxy-THC and its ester glucoronide by RIA with a cut off of approximately 2 ng/mL. The urine specimens showed low but detectable concentrations of cannabinoid metabolites; the maximum concentration detected was 6.6 ng/mL. None of the nonsmoking volunteers experienced subjective effects associated with marijuana use.