A view through the gateway: expectancies as a possible pathway from alcohol to cannabis

The aim of this study was to test the hypothesis that cannabis outcome expectancies would be more positive in adolescents who drink alcohol than in non-drinkers.

The participants in the study were 4544 11-16-year-olds attending eight secondary schools located in the north-west midlands of England.

Participants completed an anonymous self-report questionnaire that incorporated sections designed to tap adolescents' expectancies of positive and negative outcomes of alcohol and cannabis use, together with other questions relating to substance use and associated issues.

Four reliable six-item scales were derived, and used to measure positive and negative alcohol and cannabis outcome expectancies. Negative expectancies were relatively stable across age and frequency of substance use, particularly for alcohol. However, positive expectancies for both substances increased markedly with age and, independently, with frequency of use. Positive alcohol and cannabis outcome expectancies were meaningfully related to expectancies of future substance use, and to measures of problem drug use and resistance to peer influence, supporting the validity of these expectancy measures, and their possible value as diagnostic screening instruments. The main hypothesis of the study was supported: among respondents who reported never using cannabis, positive cannabis outcome expectancies increased and negative cannabis outcome expectancies decreased with increasing frequency of alcohol use.

The results are consistent with a version of the 'gateway hypothesis' for the relationship between alcohol and cannabis use (alcohol use leads to changes in cannabis expectancies and thereby to cannabis use), but a proper test of the hypothesis requires a longitudinal study.