Abstract: Research has shown that adolescent users of tobacco are much more likely to progress to use of illicit drugs than are nonusers of tobacco. This article suggests potential psychosocial reasons for the progression based on principles of Learning Theory, Theory of Reasoned Action, Health Belief Model, and Cognitive Dissonance. In addition, a neuropharmacologic causal mechanism is discussed. The existence of tobacco’s gateway function has important implications in (the nation’s) efforts to reduce illicit drug use and adolescent smoking.

Gateway drugs — drugs of entry — serve as stepping stones to illicit drug use. Tobacco use in particular has proved a strong and consistent predictor of subsequent illegal drug use. Not all adolescent cigarette smokers progress to using marijuana or cocaine, but a strong statistical link exists between tobacco use and progression to illegal drugs. Research indicates it is incredibly rare for a “hard core” drug user to bypass the initial behaviour of cigarette use prior to using illicit drugs. Nicotine has been described as an “almost essential precursor” and a “necessary intermediate” to the use of marijuana and other drugs. Studies documented the link between adolescent smoking and illegal drug use. These studies indicate tobacco use consistently precedes illicit drug use, and the association shows a clear dose response pattern. The more adolescents smoke, the more likely they are to use illegal drugs. The statistical link between adolescent smoking and subsequent illegal drug use has been described by researchers as a “striking quantitative relationship” and a “dramatic association”. The contrast particularly becomes impressive when illegal drug use prevalence rates of adolescent daily cigarette smokers are compared to nonsmokers. Results vary, depending on which illegal drug is being studied, frequency of use (daily, monthly, ever) and the grades included in the study. One study showed the relative risk for illicit drug use among one pack or more daily teen smokers consistently at 10 to 30 times greater than for nonsmokers. Surveys by the U.S. Dept. of Health and Human Services demonstrated that young daily smokers were 114 times more likely to have used marijuana than those who had not smoked. Much of the statistical link between smoking and illegal drug use results from an indirect association where both behaviours share a common etiology caused by other psychosocial and environmental factors. However, an increasing number of researchers suggest the link between adolescent smoking and subsequent illicit drug use also results from causal mechanisms. While studies document a statistical association between the two behaviours, few propose theoretical models to explain potential causal mechanisms for the association. Yet, several potential psychosocial and neuropharmacologic causal mechanisms promote tobacco’s gateway drug function.