Substances like opium and cannabis have been taken in Europe for centuries. Over the decades, the introduction and widespread use of synthetic drugs, such as LSD and MDMA (ecstasy), has created new user groups and changed the patterns of use. Drugs, old or new, do not only have an impact on the individual in form of psychological disorders, but also on society's reaction to their users. They create an illegal market with all its criminal side effects, and they trigger researchers to understand the phenomenon of drug use, changing patterns and spread. This book reflects on patterns of and changes in the use of old and new drugs; it challenges the gateway theory, critically discusses the concept of dealers, and examines strategies of harm reduction for imprisoned offenders. In addition, it offers new approaches to old problems by bridging the gap between quantitative and qualitative drug research.