Amount of self-reported illicit drug use compared to quantitative hair test results in community-recruited young drug users in Amsterdam.

Aims: To assess the dose-effect relationship between self-reported drug intake and the concentration of drugs and/or their metabolites in hair and to examine factors that may mediate this relationship.

Design And Setting: A cohort study among young drug users (YDU) in Amsterdam, the Netherlands, which began in July 2000. At intake, YDU were asked to report their average drug intake over a 2-month period.