Dutch coffee shops and trends in cannabis use.

Conflicting predictions have been made to the influence of decriminalization on cannabis use. Prohibitionists forecast that decriminalization will lead to an increase in consumption of cannabis, while their opponents hypothesise that cannabis use will decline after decriminalization. Most probably cannabis use in the Netherlands so far evolved in two waves, with a first peak around 1970, a low during the late 1970s and early 1980s, and a second peak in the mid-1990s. It is striking that this trend in cannabis use among youth in the Netherlands rather parallels four identified stages in the availability of cannabis. The number of cannabis users peaked when the cannabis was distributed through an underground market (late 1960s and early 1970s). Then the number decreased as house dealers were superseeding the underground market (1970s), and went up again after coffee shops took over the sale of cannabis (1980s), and stabilised or slightly decreased by the end of the 1990s when the number of coffee shops was reduced. Although changes in cannabis policy went along with changes in availability of cannabis and prevalence of cannabis use, it is questionable whether changes in cannabis policy were causally related to trends in cannabis use. Cannabis use also developed in waves in other European countries that did not decriminalize cannabis, as well as in the US. Consequently, trends in cannabis use seem to develop rather independently of cannabis policy.