Genetic influences have been reported for adolescent alcohol use [3], peer behaviour [19] and friendship maintenance and formation [20]. It seems plausible that the correlation between peers and adolescent alcohol use is explained partially by an overlap in genetic factors. To date, a US-based study of 14-year old twins [4] is the only twin study to examine peer influences and adolescent alcohol use. The study used a measure of peer deviance and found that the association with alcohol use was explained by common environmental influences (i.e. environmental influences that make the twins more similar), with no evidence for genetic influences. Peer alcohol use was assessed as part of a broader index of peer deviance. Given the strong association identified between peer and adolescent alcohol use, it may be an important risk factor in its own right [5–7]. Further, genetic influences have been reported for a combined measure of peer alcohol and cigarette use [19] but not for peer deviance [4], suggesting that their aetiology may be different.
