In 1809 Magendie presented to the Académie des Sciences and to the Société Philomatique the results of his first experimental work, which he carried out in collaboration with the botanist and physician Alire Raffeneau-Delille. In a series of experiments on various animals the two investigators studied the toxic action of several botanic drugs, particularly upas, nux vomica, and St.-Ignatius's bean. These experiments marked the beginning of experimental pharmacology. They were the first experimental comparisons of the similar effects produced by drugs of different botanical origin.
Magendie believed that the toxic or medicinal action of natural drugs depends on the chemical substances they contain, and that it be would to obtain these substances in the pure state. As early as 1809 he suspected the existence of strychnine, later isolated, in accord with his predictions, by Pierre Joseph Pelletier in 1819. Moreover, in 1817, in collaboration with Pelletier, Magendie discovered emetine, the active principle of the root of Carapichea ipecacuanha or ipecac.
See also Magendie's follow-up paper: Mémoire sur les organes de l'absorption chez les mammifères. Lu à l'Institut, le sept Août 1809.
Digital facsimile of the offprint of the April 1809 paper from BnF Gallica at this link.