This book contains four selected chapters on the dangers of psychoactive substances. Chapter One reviews synthetic cannabinoids and cathinones. Chapter Two is a comprehensive methodical validation of caffeine as an anthropogenic marker in water samples. Chapter Three is a cross-sectional chromatographic and pharmacogenetic study on the functional impact of CYP2D6 variants and their expression pattern. Chapter Four is a method development study on old benzodiazepine and new NPS-phenazepam. The book concludes with a bibliography.