Quitting smoking is very difficult due to nicotine’s addictive properties. There is substantial variability in nicotine addiction and relapse rates which is attributable, in part, to heritable influences. Twin studies estimate that heritable influences account for roughly 46–84% of the variability in smoking initiation and smoking persistence and as much as 75% of the variability in nicotine dependence (Sullivan and Kendler 1999; Vink et al. 2005). Other studies have shown that heritable factors account for 29–53% of the variability in withdrawal symptoms and 51–54% of the variance in quitting success (Lessov et al. 2004; Pergadia et al. 2006; Xian et al. 2003, 2005).
