Abstract: The present invention provides a method for determining recent use of cannabis, including recent use within the impairment window, following administration through inhalation, the method comprising the collection of samples of exhaled breath and whole blood separated by known intervals of time, analyzing them using appropriate analytical methods, and then calculating pharmacologic parameters associated with recent cannabis use. In particular embodiments, the method is used by employers in the routine monitoring of workplace drug policy compliance among employees and in workplace accident investigations. In some embodiments, the method is utilized by law enforcement personnel to gath-er evidence in driving under the influence investigations.