This book focuses on the critical role CYP2D6 plays in the human liver. It examines the genetic, epigenetic, physiological, pathological, and structural factors of the gene that govern the highly variable metabolism of a number of drugs in clinical use. It highlights the impact of the functional roles of CYP2D6 on clinical practice and drug development and also discusses implications for precise medicine, strategies to avoid adverse drug reactions, and paths for future research. Cytochrome P450 2D6 is a unique, valuable book focusing on a single but immensely powerful human gene. It provides the first single source of comprehensive information on CYP2D6 that serves as an important reference for medical, biomedical, pharmaceutical, and nursing researchers, practitioners, and students.