Conventional wisdom once held that the demand for addictive substances like cigarettes, alcohol, and drugs was unlike that for any other economic good and, therefore, unresponsive to traditional market forces. Recently, however, researchers from two disparate fields, economics and behavioral psychology, have found that increases in the overall price of an addictive substance can significantly reduce both the number of users and the amounts those users consume. Changes in the "full price" of addictive substances including monetary value, time outlay, effort to obtain, and potential penalties...