In traditional medicine, Cannabis sativa L. has been used for variety of reasons. Old literatures delineate that Cannabis had been used as anesthetic and analgesic, or to reduce symptoms such as cough, paralysis and so on. Although Cannabis has a long history of medical use, it is illegal in many countries including South Korea. Controversy over decriminalization of Cannabis to allow cannabis for therapeutic use has been around for many years. In order to understand current knowledge on the therapeutic use of medical Cannabis, comprehension of cannabinoids and other constituents of Cannabis is important. Here we reviewed the pharmacological effect of Cannabis and current mandatory regulation over Cannabis in many countries to suggest necessity of research on medical Cannabis.