A detailed record of plants cited during ethnopharmacological surveys, suspected of being toxic or of triggering adverse reactions, may be an auxiliary means to pharmacovigilance of phytomedicines, in that it provides greater knowledge of a "bad side" to plant resources in the Brazilian flora. This study describes 57 plant species of restricted use (abortive, contraceptive, contraindicated for pregnancy, prescribed in lesser doses for children and the elderly, to easy delivery, in addition to poisons to humans and animals) as indicated during ethnopharmacological surveys carried out among three cultures in Brazil (Caboclos-river dwellers, inhabitants of the Amazon forest; the Quilombolas, from the pantanal wetlands; the Krahô Indians, living in the cerrado savannahs). These groups of humans possess notions, to a remarkable extent, of the toxicity, contraindications, and interaction among plants. A bibliographical survey in the Pubmed, Web of Science and Dr. Duke's Phytochemical and Ethnobotanical Databases has shown that 5 out of the 57 species have some toxic properties described up to the present time, they are: Anacardium occidentale L. (Anacardiaceae), Brosimum gaudichaudii Trécul (Moraceae), Senna alata (L.) Roxb. (Fabaceae), Senna occidentalis (L.) Link (Fabaceae), Strychnos pseudoquina A. St.-Hil. (Loganiaceae) and Vernonia brasiliana (L.) Druce (Asteraceae).