The genetic epidemiology of cannabis use, abuse and dependence.

AIMS: The genetic etiology of cannabis use, abuse and dependence has elicited significant interest from genetic epidemiologists.

METHODS: Genetically informative studies, including family, twin and adoption studies that have examined the role of genetic and environmental influences on the various stages of cannabis involvement, and the genetic relationship between cannabis, licit drugs and other hard drugs, are reviewed.

RESULTS: Findings across a number of such studies have indicated that there is a genetic basis to each stage of cannabis involvement although a proportion of the genetic factors influencing individual stages may be specific to that stage. Multivariate analyses that explore the association between cannabis and licit (alcohol and tobacco) as well as hard drugs (e.g. cocaine, opioids), using multiple methodological strategies, suggest the role of common genetic and environmental influences influencing the liability to cannabis and other drug involvement.

CONCLUSIONS: The substantial evidence for the heritability of cannabis use, abuse and dependence underscore the importance of linkage and association studies that aim to find genes of etiologic significance.