1. World Health Organization (WHO). Global health observatory data: prevalence of tobacco use. Geneva: World Health Organization; 2015. Available from: http://www.who.int/gho/tobacco/use/en . Accessed 20 Nov 2015.
2. Centers for Disease Control and Prevention. Current cigarette smoking among adults—United States, 2005–2013. Morb Mortal Wkly Rep. 2014;63(47):1108–12.
3. Hasin DS, Saha TD, Kerridge BT, et al. Prevalence of marijuana use disorders in the United States between 2001–2002 and 2012–2013. JAMA Psychiatry. 2015;72(12):1235–42.
4. United Nations Office on Drugs and Crime. World drug report 2012. Vienna: United Nations Office on Drugs and Crime; 2012. https://www.unodc.org/documents/data-and-analysis/WDR2012/WDR_2012_web_small.pdf . Accessed 7 Dec 2015.
5. Hermann PC, Sancho P, Canamero M, et al. Nicotine promotes initiation and progression of KRAS-induced pancreatic cancer via Gata6-dependent dedifferentiation of acinar cells in mice. Gastroenterology. 2014;147(5):1119–33 e4.