What do we really know about cannabis? Why does it make people stoned? Does it kill off brain cells? Why do different kinds of weed have different effects? Is it addictive? Is the talk about medicinal applications genuine, or just a scam to get it legalised? Patrick Matthews journeys through a Rizla-strewn world and finds that researchers have unravelled the complexities of the plant, uncovering in the process much of the chemistry of our minds and emotions. His book is an essential read in the wake of the current debate over the decriminalisation of cannabis.