plateau around 5 cigarettes per day (20); suggesting that within the range of 1 to 5 cigarettes per day adolescents experience progressively increasing exposure to nicotine, whereas above 5 cigarettes per day smokers have reached a level of desired nicotine intake. None of the participants used nicotine replacement in the prior week and or had used bupropion (Zyban) within the past 30 days.
