Cannabis, also known as hemp or marijuana, has been used by humans for fiber, medicine, and as a psychoactive for at least 4,500 years. Its biological name is Cannabis sativa, with a subspecies, Cannabis sativa indica, used most often for recreational or medicinal purposes. The earliest milestone in the history of cannabis are charred cannabis seeds dated to 2500 BCE found on a ritual brazier in Romania. In 2008, nearly two pounds of cannabis was found buried in the tomb of a Gushi shaman who lived about 700 BCE in the Gobi Desert, northern China. Genetic analysis of the plants found they were cultivated rather than from the wild.
The most famous early users in the history of cannabis were the Hindus of India and Nepal. Soma, a drug mentioned in early Hindu texts as an intoxicating hallucinogen, may have been a reference to cannabis. Spreading with the Indo-Aryan culture from India outwards, cannabis was introduced to the Assyrians (Iraq/Syria), Scythians (Eurasian steppe), and Thracians/Dacians (Greece and the Balkans) in the 3rd and 2nd millennia BCE. The shamans of the latter culture were called kapnobatai — "those who walk on smoke/clouds." They used burning cannabis flowers to induce a state of trance. This practice is believed to have been inherited by Greek oracles and worshippers, including members of the cult of Dionysus.
Early users in the history of cannabis would have also been attracted to the plant by its positive medical properties, including the alleviation of pain, nausea, depression, and as an agent for encouraging the appetite. Modern science has uncovered additional benefits from cannabis, including the inhibition of cancer cell growth and the reduction of memory impairment in the elderly. On the negative side, cannabis use has been found to correlate with anxiety, but there is debate as to whether its role is causative or merely correlative. There are harmful chemicals in marijuana smoke, so patients consuming the drug for medical purposes often do so orally or by using a vaporizer.
After cannabis was used freely for thousands of years, a major change in the history of cannabis came in the early 20th century, when prohibitionists in the United States succeeded in getting the government to criminalize the drug, beginning with the Marihuana Tax Act of 1937. This was followed up by subsequent legislation in 1951 and 1971 (the Comprehensive Drug Abuse Prevention and Control Act of 1971). The leading figure in the criminalization of cannabis was conservative Harry Jacob Anslinger, who linked the drug to moral decline and even spontaneous murder.
From the 1970s to the present, the legality of cannabis has been a contentious issue between those arguing for the repeal of prohibition and those who wish to uphold it. Medical marijuana is allowed in several US states, in defiance of federal anti-marijuana laws. Extensive debates are ongoing at the state and federal levels.