Workplace drug testing is routinely criticized as irrational, unproductive, and even motivated by nefarious intent. This article analyzes the costs and benefits of workplace drug testing within the context of a complex business environment. Even in a drug-policy vacuum, workplace drug testing is shown to be rational under certain circumstances. The rationality of a drug-testing regime strengthens during a societal War on Drugs and weakens slightly as society transitions into a drug-enforcement regime that experiences legalization at the state level and enforcement at the national level. Throughout, however, the optimum level of workplace drug testing is likely never zero.