Cannabis presents itself as another challenge of the last decade. Better and better deciphered through in-depth studies, this drug remains a source of scientific debates. Legalized in some states, it competes with tobacco regarding the effects generating respiratory symptoms, chronic bronchitis, bronchial cancer, respiratory infections, etc. In this article we will review the pharmacology, epidemiology, clinical and prevention aspects and try to demonstrate which of these are the most effective means of prevention. This review proves once again that this drug has many hidden dangers.