Nicotine is the main addictive ingredient of tobacco. When somebody smokes a cigarette, nicotine is rapidly absorbed by the lungs and delivered to the brain. While Nutt et al’s expert panels rated nicotine (tobacco) as only the 12th most addictive substance, there are reasons to believe that nicotine is a very powerful addictive drug.
http://businesstech.co.za/news/lifestyle/115554/the-5-most-addictive-substances-on-earth/
http://businesstech.co.za/news/lifestyle/115554/the-5-most-addictive-substances-on-earth/