Use and availability of alternative healthcare products have revived in the last few years. The prevalence of supplement use in the United States is largely unknown but is thought to be widespread. In this article, four of the common substances used to treat emotional problems are reviewed. The plant or substance description, clinical indications, evidence of therapeutic efficacy, mechanisms of therapeutic actions, dosages and regimens, different commercially available preparations, and adverse effects and toxicities are described for melatonin, St John's wort, valerian, and kava-kava. That a product is "natural" does not mean that it is either safe or effective. Many supplements are potent drugs that lack sufficient data on safety, dose-response relationships, drug interactions, and purity.