Smoking is a major public health issue due to the morbidity and mortality that can be attributed to it. British cohort studies have shown, for example, that approximately half of regular smokers will die from a condition directly attributable to tobacco, such as cancer of the aerodigestive tract or respiratory disease, and that the probability of living past the age of 70 is half as high among regular smokers as among nonsmokers. Because tobacco is highly addictive, this public health issue arises as early as the initiation phase, which most often occurs during adolescence.[excerpt from chapter]