This prospective, decade-long study finds no support for the “gateway theory” that marijuana causes youth to move on to hard drug use. The study found that some youth followed the traditional gateway paradigm, starting with tobacco or alcohol and moving on to marijuana, but some reversed the pattern, starting with marijuana first. Some never progressed from one substance to another at all, upsetting the hierarchical nature of gateway theory. Neighborhood environment and individual tendency towards deviancy were the only predictors of drug use. The study emphasizes that use of drugs is associated with family and environmental circumstances, not a particular characteristic of drugs themselves.

Ralph E. Tarter et al., “Predictors of Marijuana Use in Adolescents Before and After Licit Drug Use: Examination of the Gateway Hypothesis,” American Journal of Psychiatry 163, issue 12 (December 2006): 1-7.
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