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. Nutt et al’s expert panels rated nicotine (tobacco) as the third most addictive substance.
More than two-thirds of Americans who tried smoking reported becoming dependent during their life. In 2002 the WHO estimated there were more than 1 billion smokers and it has been estimated that tobacco will kill more than 8 million people annually by 2030. Laboratory animals have the good sense not to smoke. However, rats will press a button to receive nicotine directly into their bloodstream -- and this causes dopamine levels in the brain’s reward system to rise by about 25% to 40%.