Aims: The aim of this paper is to examine the familial aggregation of cannabis use disorders and other psychiatric conditions among first-degree relatives and spouses of probands with a cannabis use disorder.
Design: Controlled family study methods.
Setting: Out-patient psychiatric clinics and the local community (same geographic area).
Participants: Two hundred and sixty-two probands with a life-time history of cannabis use disorder, alcohol dependence, anxiety disorders or no history of any disorder, and their first-degree relatives and spouses.
Measurements: Cannabis use disorders and other DSM-III-R disorders in the relatives and spouses using the Schedule for Affective Disorders and Schizophrenia.
Findings: Results reveal an elevated risk of life-time history of cannabis use disorders among siblings [odds ratio (OR: 3.6), adult offspring (OR): 6.9], and spouses (OR: 4.4) of probands with cannabis use disorders. There is a latent familial factor underlying cannabis use disorders that was shared partially with alcohol abuse/dependence. Comorbid mood and anxiety disorders aggregated independently from cannabis use disorders in families. Equal elevation in the magnitude of the association among the first-degree adult relatives and spouses of probands with a cannabis use disorder suggests the probable contribution of both environmental and genetic factors.
Conclusions: These findings support a family-based approach to drug abuse intervention and the importance of future research concerning environmental mediators of familial transmission of drug abuse.