Teenagers can become addicted to nicotine by smoking a single cigarette, a tobacco researcher has found.  By studying adolescents who smoke only occasionally, Dr. Josephe DeFranza examined how nicotine produces dependency.  He concluded that for many teens, even one exposure to cigarettes sets up a powerful reward system in the brain.  Teenagers in the study who smoked as few as three cigarettes per week could not do without these occasional smokes without feeling strong cravings and irritability.  As a result, they kept smoking, if even only occasionally.  "Most of these self-described 'social smokers' were addicted to tobacco," he says.  For those who smoked more often, of course, the cravings were more urgent.  "It's a huge mistake to start smoking," DiFranza says.  "If (teens) never start, they'll never have to worry about quitting."
sited from The Week, February 29, 2008