Candidate gene studies, including reports examining the CNR1, GABRA2, FAAH and ABCB1 genes have detected some significant associations with cannabis use but again, replication has been inconsistent.21, 22, 23 On the basis of a sample of 7452 Caucasian individuals, Verweij et al.21 found no gene-based associations between the frequency of cannabis use and 10 candidate genes identified by Agrawal and Lynskey.24 Overall, the results of candidate-gene studies are inconclusive; some associations have been replicated a few times, but failed to replicate in other studies. Moreover, findings may be further distorted due to publication bias favouring significant results.
