Dextromethorphan (DM) is an over-the-counter antitussive drug that is also used as one of the active ingredients in many cold and cough medicines. In recent years, DM has also been used in other medicines, ranging from pain relief (as either the primary analgesic or an opioid potentiater) over psychological applications to the treatment of addiction. Pharmacodynamics of DM have been gradually discovered with the elucidation of the following properties, including uncompetitive NMDA receptor antagonist, 1 and 2 sigma receptor agonists, 3 4-nACh receptor antagonist, and others. DM is transformed to its primary and active metabolite dextrorphan predominantly via the metabolic enzyme cytochrome P450 (CYP) 2D6. Hence, DM is the first-choice substrate for CYP2D6 phenotyping because it is relatively safe and possesses many favorable pharmacokinetic characteristics for a marker substrate. This book aims to meet the needs of basic molecular biochemists, pharmacologists, pharmacists, medical students, clinical practitioners and scientists, as well as broad readers who wish to understand the pharmacology of DM and its clinical uses. The contributing authors are basic scientists, pharmacologists, pharmacists and on-service physicians in neuro-psychiatric, anesthesiologic and hepatologic fields from the Czech Republic, Austria, the United States, and China. As a collection of masterpieces by well-known experts, this book presents current research in the study of DM, focusing on its pharmacology, clinical uses and health effects. Topics discussed in this compilation include the new pharmacological application of DM; pharmacogenetics of DM; pharmacodynamics and toxicological profiles of DM; long cutaneous block by lidocaine and DM; toxic and beneficial effects of DM on the central nervous system; pharmacokinetics of DM and drug interactions; DM as a probe drug for CYP2D6 and CYP3A4 phynotyping; evaluation of CYP2D6 in DM-herb interactions; and clinical uses and health effects of DM.