The chronic abuse of many drugs produces both marked tolerance and physical dependence. Marked tolerance to cannabis has been observed in experimental animals and humans. However, reports of physical dependence, as characterized by significant withdrawal symptomatology upon cessation of chronic cannabis exposure, has not been well established or clearly defined in any species. The abuse potential of cannabis is more readily observed in humans than in experimental animal investigations. This may be due to the physiochemical characteristics of cannabis or delta 9-THC, which complicates this type of animal experimentation. It is more likely that the greatest dangers of cannabis abuse involve the pharmacological effects of the drug upon the central nervous system and other organs, rather than the development of dependence.