Under double influence: assessment of simultaneous alcohol and cannabis use in general youth populations.

BACKGROUND/AIMS We assessed to what extent adolescents use alcohol and cannabis simultaneously and expanded previous research by estimating the proportion of all events of cannabis use that had occurred in relation to drinking. How the prevalence of this form of polysubstance use co-varied with the overall level of alcohol and cannabis use in different countries was also examined. METHOD We analysed individual level data from a survey of 14-20 year-olds in Norway (n=16 813) and population level data from the 2003 ESPAD study on substance use among 15-16 year-olds in 35 European countries. RESULTS The prevalence of simultaneous intake of alcohol and cannabis in the past year among Norwegian youth was 7%. The overall prevalence of cannabis use was only slightly higher (8%), implying that a majority (82%) of the cannabis users had taken the drug in combination with alcohol. Moreover, in about 80% of all incidents of cannabis use, alcohol had been consumed as well. Correspondingly, a majority of the cannabis users in most of the countries in the ESPAD study had used the drug in combination with alcohol. Such simultaneous polysubstance use was more prevalent in countries where cannabis use was relatively widespread and alcohol rather frequently consumed. CONCLUSION Because adolescents most often combine cannabis with alcohol, their use of the drug may be more harmful than assumed. The results also indicate that cannabis is a complement rather than a substitute for alcohol, suggesting that policies that reduce adolescent drinking may reduce the use of cannabis as well.