Published: 15 November 2011
Over the past 10 years, a number of European countries have changed their drug laws regarding cannabis, and many of these have prevalence estimates for the use of the drug before and after the legal change. A simple before– after comparison using these data can explore whether an observable change in prevalence can be seen in the years after law change. As cannabis use is concentrated among the younger age groups, the analysis was performed using prevalence data for 15- to 34-year-olds. In the graph, last year cannabis prevalence is plotted against time, with zero on the horizontal axis representing the year of legal change. Because of differences between countries in the year in which they changed their laws and in the extent of their survey data, the trend lines cover varying times.
Countries increasing the penalty for cannabis possession are represented in the graph by dotted lines, and those reducing the penalty by solid lines. The legal impact hypothesis, in its simplest form, states that a change in the law will lead to a change in prevalence, with increased penalties leading to a fall in drug use and reduced penalties to a rise in drug use. On this basis, the dotted lines would fall and the solid lines would rise after the change. However, in this 10-year period, for the countries in question, no simple association can be observed between legal changes and cannabis use prevalence.
NB: Legal changes took place in 2001–06; see Chapter 1 and ELDD Topic overview on possession.