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What is THC?

thc molecule
Molecule of tetrahydrocannabinol, or THC, the main mind-altering ingredient found in the Cannabis plant.
Credit: style-photography.de | Shutterstock

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 heroin, 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. On average, the effects last about two hours, and kick in 10 to 30 minutes after ingestion. Psychomotor impairment may continue after the perceived high has stopped, however. These effects of marijuana make it a popular drug. In fact, it is considered one of the most commonly used illicit drugs in the world. But these effects also concern mental health advocates. THC can trigger a relapse in schizophrenic symptoms, according to the National Institute on Drug Abuse.

Another possible risk of consuming THC comes in the form of impaired motor skills. Marijuana may impair driving or similar tasks for approximately three hours after consumption, reports the National Highway Traffic Safety Administration. It is the second-most common psychoactive substance found in drivers, after alcohol. People taking medical marijuana are instructed not to drive until it has been established that they can tolerate it and conduct motor tasks successfully.

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 secreted 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. The National Highway Traffic Safety Administration reports that the average THC concentration in marijuana is 1 to 5 percent; in hashish, it is 5 to 15 percent, and in hashish oil, it averages at 20 percent. THC in recreational doses of marijuana is highly variable and the lower the THC content in the marijuana, the more the user must consume to produce the desired effects. In terms of medical marijuana, the initial starting dose is 2.5 mg twice a day.

THC can be extracted from marijuana, or synthesized, as is the case for the FDA-approved drug dronabinol. Dronabinol is used to treat or prevent the nausea and vomiting associated with cancer medicines and to increase the appetites of people with AIDS, according to the U.S. National Library of Medicine. It is a light yellow resinous oil.

Jessie Szalay contributed to this article.

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