This study aimed to identify undesirable and toxic effects of plants used in Guinean traditional medicine. Materials and Methods:We surveyed 131 traditional practitioners in 2 prefectures of Guinea about their knowledge and experience with adverse or toxic events associated with the medicinal or nonmedicinal use of plants, collecting samples of these plants for botanical analysis. Results: Ethnobotanically, 54 species from 33 botanical families were identified. The main species identified as having adverse or toxic effects were Erythrophleum suaveolens, Dichapetalum toxicarium, Mucuna pruriens, Datura metel, Anthostema senegalense, Gardenia erubescens, Detarium senegalense and Strophanthus hispidus. Conclusion:This work provides a basis for identifying and establishing a database on the toxicity of plants used for medicinal and non-medicinal purposes in Guinea.