1. The WHO tobacco free initiative Geneva, Switzerland 2014 http://www.who.int/tobacco/mpower/tobacco_facts/en/
2. Nicotine addiction;Benowitz;N. Engl. J. Med,2010
3. Non-cigarette tobacco products: what have we learnt and where are we headed?;O'Connor;Tob. Control,2012
4. The WHO tobacco free initiative Geneva, Switzerland 2014 http://www.who.int/tobacco/communications/statements/eletronic_cigarettes/en/
5. Gilbert , H.A. inventor; Smokeless non-tobacco cigarette 1965