Alternative and complementary medicine have been enjoying a recent growth in popularity in the United States. People are increasingly likely to consult them in an attempt to treat their illnesses. While this may be a positive trend, there is also an enormous potential for harm, depending on what illness is being treated and the type of treatments being sought. Given the myriad of alternative and complementary treatments available, both consumers and practitioners of health care are hard pressed to select appropriate, effective, and safe treatments. Although treating illness and creating psychological effects using plants are ancient practices, scientific developments in the past few decades allow us to now look at these phenomena in a different way. As our understanding of the nervous system advances, so does our understanding of psychoactive drugs that alter it. We can now begin to explain how the psychoactive effects occur, from molecular up to behavioral levels. Whereas much of alternative and complementary medicine is criticized for a lack of empirical research, there seems to be a wealth of research done on plant medicines. In the course doing research in pharmacology and neuroscience, it became apparent that a large body of research existed concerning psychoactive herbal medicines. However, it was also apparent that few, if any, had comprehensively and thoroughly organized and integrated this research into a single source. This text is primarily aimed to benefit researchers and health care practitioners. Since health care practitioners find many of their patients using over-the-counter herbal medicines, they need a source to help them anticipate how these herbs will interact with their patients' illnesses and treatments. Alternatively, they may wish to incorporate herbal medicines into a patient's treatment regimen whenever appropriate. Toward this end, this book details the chemical constituents, mechanisms, and physiological effects of psychoactive plant drugs. Further, information is given on any controlled clinical trials that address the safety and efficacy of psychoactive herbal medicines. Researchers in this field will also benefit from the broad summary of data collected here, incorporating biochemistry, pharmacology, physiology, cognition, and behavior. From this perspective, future avenues for research often become apparent. Ultimately, this book is intended to further the cause of herbal medicines. If they are properly researched and the public is properly educated about their effects and uses, herbal medicines will be an asset to us, rather than a liability.