Route of drug use and its implications for drug effect, risk of dependence and health consequences.

Route of administration has a profound, but often overlooked, influence on the actual experience of the drug use itself, on the risk of resulting development of dependence, and on the nature of the harms to which drug users are exposing themselves. These three areas are reviewed. The influence of route of administration on drug effect is considered first with regard to overall effectiveness of absorption, and also with regard to speed of onset of effect. The implications for risk of dependence cover animal and human laboratory studies of reinforcement schedules, epidemiological studies, the attitudes of drug users themselves to the different routes of possible drug use and associated dependence risk and the postulated influences on progression to dependence. Finally, the relationship between route of drug use and health sequelae is explored for the three most widely used routes of administration of illicit drugs-snorting, smoking and injecting.