This updated and revised second edition on substance abuse in adolescents and young adults provides information on this global public health topic. We cover a wide variety of subjects within the paradigm of drug abuse and agree with the 21st century message of integrating substance abuse management with primary care services. The editors thank the many experts who so graciously and lambently provided their time and knowledge in these areas. The editors hope that the readers of this treatise find useful and beneficial information that will help them in their work seeking to understand and ameliorate the negative effects of these plants of paradise and of other chemicals that are part of the drug addiction pharmacopeia of the 21st century. The science of this field continues to evolve and this edition looks at a wide variety of concepts in this regard----including neurobiology, genetics, the role of the primary care clinicians, the US opioid epidemic, and psychosocial management. Specific drugs of abuse include tobacco, cannabis, alcohol, opioids, prescription drugs, illicit stimulant drug abuse, hallucinogens, and date rape drugs. We also look at concepts related to prenatal drug exposure, substance abuse in adolescent females, co-occurring substance use with psychiatric disorders, prescription stimulant abuse in college students, and performance enhancing drugs in sports. We conclude with a consideration of new drugs of abuse in the 21st century, the societal burden of substance abuse, and the pros as well as cons of drug legalization.