Pharmacovigilance is the science of monitoring the effects of pharmaceutical products after they have been licensed for use, especially in order to identify and evaluate previously unreported adverse reactions. Herbal medicines are traditionally viewed as safe due to their natural origins, but reports have shown several herbs can cause adverse reactions. Systematic pharmacovigilance of herbal medicines is needed to build a reliable understanding of their safety and inform guidelines for their safe use. Problems encountered include herbs containing undeclared drug ingredients, misidentification of plant species, and interactions between herbs and conventional drugs.