1. The World Health Organization: Tobacco. 2018.
http://www.who.int/news-room/fact-sheets/detail/tobacco
. Accessed 12 May 2018.
2. Centers for Disease Control and Prevention: Smoking and Tobacco Use. 2018.
https://www.cdc.gov/tobacco/data_statistics/fact_sheets/fast_facts/index.htm
. Accessed 12 May 2018.
3. The World Health Organization: Tobacco Free Initiative fact sheet about health benefits of smoking cessation. 2018.
http://www.who.int/tobacco/quitting/benefits/en/
. Accessed 12 May 2018.
4. Centers for Disease Control and Prevention: Quitting Smoking. 2017.
https://www.cdc.gov/tobacco/data_statistics/fact_sheets/cessation/quitting/index.htm
. Accessed 12 May 2018.
5. U.S. Department of Health and Human Services: Treating tobacco use and dependence: 2008 update. 2008.
https://www.ahrq.gov/professionals/clinicians-providers/guidelines-recommendations/tobacco/index.html
. Accessed 12 May 2018.