The familial aggregation of substance use disorders was investigated in families of probands with opioid, cocaine, cannabis, and alcohol abuse, and a direct association was found between drug disorders in probands and similar disorders affecting their relatives [55]. Relatives of probands with opioid use disorders were ten times more likely to have opioid related disorders (adjusted odds ratio (OR) 10.2, 95% CI: 3.2-32.6) [55]. In addition the risk for relatives was also higher for other substance use disorders when the proband is using such substances including cannabis (adjusted OR 5.8, 95% CI: 2.6-12.9), and cocaine (OR 4.4, 95% CI: 1.5-13.2) providing evidence for genetic susceptibility to substance use disorders [55].
