[영문]This paper uses information about prime age individuals living in Amsterdam to study the dynamics in the use of tobacco, cannabis, and cocaine. The analysis examines transitions from non-use to use, as well as transitions from use to non-use. Particular attention is given to the effect of the age of onset on quitting behavior. The empirical analysis shows that for most of the drugs investigated, the earlier individuals start using a particular drug the less likely they are to stop using that drug