Consumed for a wide range of reasons, substances that alter a person's mood and mind are widespread in most societies. Although many such substances initially had been valued for their medicinal properties, their usage can have health-endangering consequences, including habit formation. The misuse or abuse of legal and illicit drugs and alcohol engender numerous public health concerns over time. This analytical volume examines the physical, ethical, and public policy issues that have arisen as the result of excessive and inappropriate substance use.