Co-occurring (i.e., concurrent or simultaneous) cannabis and tobacco use may have important treatment implications (Agrawal et al., 2012; Peters et al., 2012; Ramo et al., 2012). Studies have consistently demonstrated that individuals who use both cannabis and tobacco report more severe cannabis use than individuals who use cannabis only (Agrawal and Lynskey, 2009; Agrawal et al., 2009; Caldeira et al., 2008; Coffey et al., 2003; Degenhardt et al., 2001; Heffner et al., 2008; Patton et al., 2006; Swift et al., 2008; Timberlake, 2009), although studies have been less consistent on whether individuals who use both have more severe tobacco use than those who smoke tobacco only (Agrawal et al., 2008b; Degenhardt et al., 2010; Patton et al., 2005; Timberlake et al., 2007; Timberlake, 2009). Use of tobacco in addition to cannabis negatively affects cannabis treatment outcomes (de Dios et al., 2009; Gray et al., 2011; Haney et al., 2012; Moore and Budney, 2001) and may have a negative impact on tobacco treatment outcomes (Abrantes et al., 2009; Ford et al., 2002; Gourlay et al., 1994; Haskins et al., 2010; Hendricks
