Cannabis 101 | National Geographic

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[Narrator] Cannabis, it's the most frequently used illicit substance in the United States and arguably, one of the most controversial. Cannabis, or marijuana, is a drug derived from certain strains of the plant cannabis sativa. The plant's flowers and leaves contain chemical compounds called cannabinoids, which produce cannabis's mind-altering effects.

This high is largely caused by the cannabinoid called tetrahydrocannabinol, or THC. When THC from cannabis is ingested or inhaled, it overwhelms the body's natural levels of THC in the cardiovascular and central nervous systems. In the brain, THC attaches to neurons that send information via chemicals known as neurotransmitters.

The THC decreases the amount of neurotransmitters the neurons produce, thereby decreasing the amount of information transmitted. This results in psychoactive effects such as lack of coordination, memory loss, hallucinations, and increased appetite. Because of some of the psychoactive effects, cannabis had been used for medicinal purposes for thousands of years.

Then around the 20th Century, cannabis became more accessible and more widely used for recreational purposes. But by the late 1960s, the use and possession of cannabis became illegal in many countries due to debate surrounding the drug's effects.

Opponents state that the dangers of cannabis include inducing heart attacks, decreasing sperm count, and stunting brain development, particularly in teenagers. Proponents, especially of medicinal marijuana, cite benefits including treating seizures, relieving chronic pain, and preventing nausea induced by chemotherapy.

Because of cannabis's costs and benefits, many countries continue to wrestle with how to best approach and regulate the controversial substance.