Psychoactive drug use is not just a phenomenon of the 20th century; many different types of drug have been used throughout recorded history. In this chapter we will outline the main classes of psychoactive drug. We are able to do this in a single chapter because, despite there being thousands of different drugs, they can be classified in a few main groups (Table ). The crucial role of neurotransmitters will also be described because psychoactive drugs alter mood and behaviour by modifying nerve activity in various ways
