The evaluation of the enzymatic activities of CYP2A6 in in vitro and in vivo experiments has shown that CYP2A6 polymorphisms can alter or enhance the pharmacokinetics of nicotine according to their structure (deleted/decreased or full function), thus confirming their propensity to predispose to or protect individuals from nicotine dependence [19]. This evidence concerns the gene CYP2A6 and nicotine dependence.