While there are studies that argue that cannabis is harmful, there is no substantial proof of many of the harmful effects it is accused of having. Indeed, there are many studies that claim it does not have these harmful effects. For example, a 15-year John Hopkins University study published in May 1999 found "no significant differences in cognitive decline between heavy users, light users, and non-users of cannabis."1 It is also claimed by many researchers that while cannabis has some potentially harmful effects, it is far less harmful then tobacco and alcohol2. Cannabis is also known to have medicinal qualities, such as in relieving pain for MS sufferers. In California, for example, it is possible to obtain a "medical marijuana" card. 1  2 The Economist. (2010, November 2). Scoring Drugs. Retrieved July 20, 2011, from The Economist: