MARIJUANA

The history of marijuana use reaches back farther than many would guess. Cultivation of the Cannabis sativa plant dates back thousands of years. The first written account of cannabis cultivation (ostensibly used as medical marijuana) is found in Chinese records dating from 28 B.C. That means Chinese cultures were growing marijuana more than 2,000 years ago. However, the plant may have been cultivated long before then -- there have been reports of a nearly 3,000-year-old Egyptian mummy containing traces of THC, the main psychoactive chemical in marijuana.
Cannabis sativa is perhaps the most recognizable plant in the world. Pictures of the ubiquitous green cannabis leaf show up in the news media, textbooks and drug-prevention literature, and the leaf's shape is made into jewelry, put on bumper stickers and clothing and spray-painted on walls. The leaves are arranged palmately, radiating from a common center like the fingers of a hand spreading apart. Although most people know what the cannabis plant looks like, they may know very little about its horticulture.

Cannabis sativa is believed to be a native plant of India, where it possibly originated in a region just north of the Himalayan mountains. It's a herbaceous annual that can grow to a height of between 13 and 18 feet (4 to 5.4 meters). The plant has flowers that bloom from late summer to mid-fall. Cannabis plants usually have one of two types of flowers, male or female, and some plants have both. Male flowers grow in elongated clusters along the leaves and turn yellow and die after blossoming. Female flowers grow in spikelike clusters and remain dark green for a month after blossoming, until the seed ripens. Hashish, which is more powerful than marijuana, is made from the resin of the cannabis flowers.

Marijuana plants contain more than 400 chemicals, 60 of which fit into a category called cannabinoids. THC is just one of these cannabinoids, but it's the chemical most often associated with the effects that marijuana has on the brain. Cannabis plants also contain choline, eugenol, guaicacol and piperidine. The concentration of THC and other cannabinoids varies depending on growing conditions, plant genetics and processing after harvest. You'll learn more about the potency of THC and the toxicity of marijuana next.