Modest to moderate correlations (ranging from 0.16 to 0.35) were found between early conduct problems and tobacco, alcohol and cannabis use in young adulthood. These phenotypic correlations are broadly comparable to earlier established correlations between externalizing/conduct problems in early adolescence and later tobacco, alcohol and other substance use [20–21]. Moderate correlations between conduct problems and cannabis use have also been reported cross-sectionally [10]. This combination of findings may suggest that the strength of the association between early adolescent behavioural problems and subsequent substance use is not attenuated much over time.
