THC, or tetrahydrocannabinol, is the chemical responsible for most of marijuana's psychological effects. THC changes behavior by binding — fitting together like a lock and key — to receptors on nerve cells, which then respond with a change in activity.
Cannabinoid receptors are concentrated in certain areas of the brain associated with thinking, memory, pleasure, coordination and time perception. There are also cannabinoid receptors on nerves in other parts of the body. THC relieves pain, but it doesn't bind to the same receptors in the brain as opioids such as heroine, morphine and other drugs derived from the poppy plant.
THC stimulates cells in the brain to release dopamine, creating euphoria. It also interferes with how information is processed in the hippocampus, which is part of the brain responsible for forming new memories. THC can induce hallucinations, change thinking and cause delusions. These effects of marijuana make it a popular drug, but they also concern mental health advocates. THC can trigger a relapse in schizophrenic symptoms, according to the National Institute on Drug Abuse.
A debate continues on marijuana's benefits as a medicine. During a 2004 congressional testimony, a doctor speaking on behalf of the FDA said marijuana as a “botanical product” is difficult to test for efficacy and safety because the proportions of active chemicals can range greatly from plant to plant. This, he said, can also cause problems for patients trying to use marijuana. But he added that the FDA “will be receptive to sound, scientifically based research into the medicinal uses of botanical marijuana and other cannabinoids.”
THC is one of many compounds found in the resin excreted by glands of the marijuana plant. More of these glands are found around the reproductive organs of the plant than on any other area of the plant. Other compounds unique to marijuana, called cannabinoids, are present in this resin and may lessen the effect of THC.
When THC is exposed to air, it degrades into cannabinol, a cannabinoid which has its own psychological effects. THC concentration also depends on the cultivation of the marijuana plant, known scientifically as Cannabis sativa L.
Cannabis that has a minimal amount of THC — up to 1 percent — is cultivated as hemp. Some strains of Cannabis can have as little as 0.3 percent THC by weight. In other strains, THC makes up 20 percent of the weight in a sample. THC can be extracted from marijuana, or synthesized as is the case for the FDA-approved drug dronabinol.
- Marijuana: Facts about Cannabis
- Effects of Marijuana
- Medical Marijuana: Benefits vs. Risks
- What is Hemp?