Co-occurring cannabis use disorders and nicotine dependence, relative to cannabis use disorders only, were associated with a higher prevalence of bipolar disorder, Clusters A and B personality disorders, and narcissistic personality disorder, while, relative to nicotine dependence only, they were associated with a higher prevalence of bipolar disorder, anxiety disorders, and several personality disorders. The association of co-occurring cannabis use disorders and nicotine dependence with a higher prevalence of several psychiatric disorders is consistent with findings of systematic reviews that have reported an association of co-occurring cannabis and tobacco use with more severe clinical problems (Agrawal et al., 2012; Peters et al., 2012; Ramo et al., 2012) and may have immediate treatment implications. Individuals with co-occurring cannabis and tobacco use have demonstrated poorer cannabis treatment outcomes than do individuals who use cannabis only (de Dios et al., 2009; Gray et al., 2011; Moore and Budney, 2001), although evidence is less consistent on whether they demonstrate poorer tobacco treatment outcomes than individuals who use tobacco only (Abrantes et al., 2009; Ford et al., 2002; Gourlay et al., 1994; Haskins et al.,
