1. 1. World Health Organization Tobacco Free Initiative. Electronic cigarettes (e-cigarettes) or electronic nicotine delivery systems statement: WHO, Geneva. 2014. Available at URL: http://www.who.int/tobacco/communications/statements/eletronic_cigarettes/en/index.html. Accessed June 2014.
2. 2. Trtchounian A, Willams M, Talbot P. Conventional and electronic cigarettes (e-cigarettes) have different smoking properties. Nicotine Tob Res 2010;12:905-12.
3. 3. Williams, M, Talbot P. Variability among electronic cigarettes in the pressure drop, airflow rate, and aerosol production. Nicotine Tob Res 2011;13:1276-83.
4. 4. Adkison SE, O'Connor RJ, Bansal-Travers M, Hyland A, Borland R, Yong HH, et al. Electronic nicotine delivery systems: international tobacco control four country survey. Am J Prev Med 2013;44:207-15.
5. 5. Medicines and Healthcare Products Regulatory Agency. Nicotine containing products. London, UK: MHRA, 2013. Available at URL: http://www.mhra.gov.uk/Safetyinformation/General safety information and advice/Product specific information and advice/Product specific information andadvice%E2%80%93M%E2%80%93T/Nicotine Containing Products/index.htm. Accessed November 2013.