Marijuana is the common name for cannabis sativa (i.e. cannabis). Medical cannabis or medical marijuana refers to the cannabis strains that are harvested and used for medicinal purposes.
Cannabis is a flowering hemp plant with three main species: cannabis sativa, cannabis indica and cannabis ruderalis. These plants grow indigenously in temperate and tropical climates. The dried leaves, flowers, stems and seeds of the cannabis plant have been long used for hemp fiber, seeds and seed oils, and for medicinal purposes.
It’s hard to say exactly where and when the cannabis plant originated but it’s been cultivated for its medicinal properties for millennia. Some documents show evidence of its origins in central Asia while other ancient literature documents point to its origins in China. In either case, cannabis is one of the world’s oldest cultivated plants, with documented evidence of the plant being used for various medicinal purposes in China since 2800 BCE.
According to the College of Family Physicians of Canada (CFPC), medical marijuana is a popularized term that “refers to dried cannabis dispensed or otherwise obtained and used either for supervised medical purposes or for self-medication”.
 Authorized Dried Cannabis For Chronic Pain And Anxiety. College of Family Physicians of Canada, Sept. 2014. Web. 21 Oct. 2014.