Many efforts are being made to find biomolecules extracted from plants to be useful therapeutic agents to replace the drugs traditionally used in clinical medicine with known side effects and high financial investment, thus offering greater safety and less risk to the population. However, the presence of toxic substances such as alkaloids, amino acids, amides, glycosides, saponins, and tannins are the main reasons for the poisonous activity of some medicinal plants. In this sense, understanding plants constituents and lethal doses can be important source in managing several diseases in human life. This review aimed to present extracts, fractions, and/or compounds of plants of Brazil and Asia regions that have reported toxicity to in vitro and in vivo models. The results presented here contribute to warning the population about the toxicological characterization of some plants, however, further high‐quality studies are needed to firmly establish the clinical efficacy of the plants (or compounds).