Moreover, gender comparisons in the present study showed that cannabis use was more frequent in males than in female patients, and the same trend was found regarding alcohol use. These differences suggest that our decision to include patients who use non-opioid substances in the study maximised the odds for detecting genetic associations more in males than in females. However, associations between the DRD2 A1 allele and cannabis use disorders have not been published. Moreover, nonspecific genetic factors account for a larger fraction of the variance of cannabis use in females (59%)[3] than in males (34%) [4]. Male-limited associations of the DRD2 A1 allele with alcohol dependence [26] and tobacco smoking [27] have been reported previously.
