Cannabis sativa (marijuana) has been used by humans for centuries, largely for its psychological effects. Currently, it is the most widely used illicit substance in the world, and there is heated public debate about whether it should be legalized, or at least decriminalized, in a number of countries. There is also considerable public and commercial interest in its medicinal properties, and in hemp as an environmentally friendly plant with numerous potential uses. This discussion needs to be informed by a consideration of the effects of cannabis on the human brain, notably its effects on cognition, and its potential to cause psychotic symptoms, particularly in vulnerable individuals. Recent advances in our understanding of the human cannabinoid system, and methodologically robust epidemiological, clinical and experimental studies of the effects of cannabis in humans, allow us to understand better how cannabis exerts both its beneficial and its adverse effects.

It has been known for many years that people who suffer psychotic illness are far more likely to consume cannabis than the general population, and there has been much dispute about the reasons for this. Unfortunately, until recently there were relatively few data available to inform this debate. The situation has changed greatly over the last decade with the publication of new basic and clinical studies. Therefore, this book provides a comprehensive and up-to-date overview of the psychiatry and neurobiology of cannabis, with particular emphasis on psychotic disorders.