Marijuana Use Rates and Decriminalization
"In California and Ohio, surveys before and after decriminalisation showed that cannabis use increased, but not at a greater rate than in US states which had not decriminalised cannabis. Single (1989) also reviewed data from two large US national surveys of drug use in the 1970s that compared rates of cannabis use in states which had and had not decriminalised cannabis. He found that the prevalence of cannabis use increased in all states, with a larger increase in those states which had not decriminalised (Single, 1989)."
Donnelly, Neil; Hall, Wayne; Christie, Paul, "Cannabis Expiation Notice Scheme on levels and patterns of cannabis use in South Australia: evidence from the National Drug Strategy Household Surveys 1985–1995," Department of Health and Aged Care (Canberra, Australia: May 1998), p. 12.