Cannabis and tobacco smoking frequently co-occur (Grant et al., 2004). A proportion of this correlation between cannabis involvement and cigarette smoking has been attributed to genetic influences (Agrawal et al., 2012), with genetic correlations ranging from 0.31 in an adolescent sample to 0.82 (in adults) (Huizink et al., 2010; Neale et al., 2006; Young et al., 2006). One twin study also noted that while cannabis and nicotine dependence are influenced by different genetic factors, the correlation between these factors is 0.82 (Kendler et al., 2007).
