The level of comorbidity between alcohol dependence and smoking was particularly high, and both alcohol dependence and habitual smoking clustered in families. Specifically, the investigators found that siblings of an alcohol-dependent proband were at 1.7 times higher risk of becoming habitual smokers than were siblings of people who were not dependent on alcohol. In addition, habitual smoking in alcohol-dependent probands further increased their siblings’ risk of becoming habitual smokers by a factor of 1.8 (Bierut et al. 1998, 2000). These findings provide further evidence of both common and drug-specific influences in the development of alcohol dependence and habitual smoking.
