SLC6A4 and nicotine dependence: The aim of this paper was to delineate whether STin2 polymorphism of the SLC6A4 gene is associated with a) tobacco use disorder, b) successful smoking cessation, c) smoking characteristics, including age at onset of tobacco use, duration of illness, lifetime cigarette consumption, years of smoking, severity of nicotine dependence, and d) comorbid substance use disorders, including alcohol and sedative abuse.