and historical overview -- Phytochemistry -- St. John's Wort and its active principles in depression and anxiety - A critical analysis of receptor binding studies -- Effects on transmitter uptake and their cellular and molecular basis -- Modulation of neurotransmitter release and metabolism -- Efficacy in behavioural models of antidepressant activity -- Comparative preclinical antidepressant activity of isolated constituents -- Hyperforin and efficacy in animal models for anxiety and cognition -- Pharmacokinetics and biopharmaceuticals -- Clinical efficacy in depression -- Clinical efficacy of St. John's Wort in psychiatric disorders other than depression -- Side effects and drug interactions -- Endocrinology of St. John's Wort extract. Hypericum extract preparations are used extensively in many countries to treat mildly to moderately depressed patients. While this was based previously on traditional experience, extensive research over the last 10 years has given a broad preclinical and clinical basis to justify the use of Hypericum as an antidepressant. This book reviews the available data related to the biochemical, functional, and behavioural pharmacology of Hypericum and its active constituents. The clinical chapters overview the evidenced basis for its use as an antidepressant, initial data in anxiety and somatoform disorders, and the site effect profile of Hypericum and its possible relevant drug interactions. The known pharmacokinetics of the relevant constituents and the biopharmaceutical quality of commercially available Hypericum preparations are also discussed.