Cannabis has a history for medical use that spans thousands of years and many cultures. The beginnings of its use by humans are very difficult to trace, because it was cultivated and consumed long before the appearance of writing. According to archeological discoveries, it has been known in China at least since the Neolithic period, around 4000 BCE.
The Emperor of China, Shen Nung, also the discoverer of Tea and Ephedrine, is considered to be the first to have described the properties and therapeutic uses of Cannabis in his compendium of Chinese Medicinal Herbs written in 2737 BCE. It showed Cannabis mainly used as a medication for rheumatism, gout, malaria, and absent-mindedness.
Until the mid 19th Centrury, all medicines were plant-based - and Cannabis was the most widely used of those plants. To this day, the efficacy of Cannabis remains proven for treating a wide range of medical conditions that modern pharmaceuticals still cannot treat - or they do so with horrendous 'side' effects, that aren't present with Cannabis.