Observation of pharmacovigilance is a descriptive and analytical study of a drug side effect. This is a multidisciplinary, multifactorial work in which the pharmacologist determines the nature of the adverse effect, classifies drugs according to the order incrimination and advises on the management of the side effect drug, based on the updated vers ion of the French method of accountability and knowledge in clinical and pharmacology. The method of writing a pharmacovigilance observation accredited by Clinical Pharmacology and Toxicology department of the UHC Ibn Rushd of Casablanca allows to study the adverse effects as a whole and based on certain concepts that are often ignored such excipients effect notorious drug interactions or occurrence mechanism of adverse drug reactions