There are a lot of stories as to why we have cannabis and drug prohibition but to really understand the concept we need to start at the beginning.
Religious intolerance was a motivation for drug prohibition in Christian Europe. In a move interpreted as support for the efforts of the Spanish Inquisition against the Arabs, in a 1484 fiat Pope Innocent VIII banned the use of cannabis. The persecution of heretics in the form of witch hunts also gathered momentum around this time, and frequently targeted users of medicinal and hallucinogenic herbs. The Inquisition proceeded apace in Meso-America and South America, where peyote (péyotl), ololiúqui, toloáche, teonanácatl and other sacred plants of the Mexican culture were prohibited as works of the devil.
Free Cannabis,End Prohibition