The comorbidity between nicotine dependence and alcohol abuse/dependence is well documented in the literature [True et al., [1999]; Daeppen et al., [2000]; John et al., [2003]; Falk et al., [2006]]. Nicotine dependent individuals are at increased risk for misusing a variety of other psychoactive substances [Dani and Harris, [2005]; Degenhardt et al., [2007]]. A recent large-scale twin study indicated that approximately two-thirds of the genetic risk factors for nicotine dependence were substance specific in their effect while one-third were non-specific and increased risk for abuse of a range of other psychoactive substances [Kendler et al., [2007]]. We were therefore interested in testing whether these variants in the α5 and α3 nicotinic receptors were associated solely with smoking and nicotine dependence or also with misuse of either another common licit (alcohol) or an illicit psychoactive substance (cannabis).
