I define psychoactive substances as those that alter the state of consciousness of the user. These effects may range from the mild stimulation caused by a single cup of tea or coffee to the powerful mind-altering effects induced by hallucinogens such as LSD or certain mushrooms, in which profound changes may occur in the perception of time, space and self. This book is neither an assault on the use of psychoactive substances nor an extended eulogy extolling their use. The use of such substances is simply a fact of life; people have always used them and, no doubt, they always will. I have tried to give a balanced and, as far as is possible, impartial account. Finally it should be stated that this book is designed to provide historical and cultural information concerning psychoactive substances. It is not intended to be a guide to the use of drugs. Ingestion of some of these substances may be harmful or even fatal.