A gateway drug is distinguished by sequence (gateway drug is used prior to other drugs), association (use of the gateway drug is associated with an increased likelihood of using other drugs) and, controversially, causation (use of the gateway drug has a causal influence on use of other drugs) (14;15). Historically, while the most frequent debate surrounds the role of cannabis as a gateway drug for other illicit psychoactive substances, cigarette smoking may serve as a gateway drug for cannabis use. For example, Yu and Williford (16), in their study of 16-24 year olds found that alcohol and cigarettes served as a gateway to cannabis use. Even in former daily smokers, risk of developing cannabis dependence is elevated (17) suggesting that tobacco exposure, particularly cigarette smoking increases the likelihood of cannabis use (18). These findings require further study, particularly to examine the potential role of confounders, such as conduct problems and other externalizing psychopathology (18).
