Tetrahydrocannabinol (THC)

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Tetrahydrocannabinol, or THC, is a chemical found in the Hemp plant, Cannabis Sativa, that causes the Psychoactive effects in Marijuana, Bhang, Hashish, and Ganja. Hashish is derived from the resin that oozes from the flowering tips of the female plant; bhang comes from the dried leaves and flowering shoots of the female plant; and ganja comes from small leaves. THC is one of the three natural cannabinoidschemical constituents of Cannabis the other two being cannabinol (CBN) and cannabidiol (CBD).

As of 2000, marijuana is the most commonly used nonlegal drug in the United States. Its usage peaked during the late 1970s, when about 60 percent of high school seniors reported having tried marijuana, with 11 percent reporting daily use. Usage has declined since 1979; as of 1999, 2 to 3 percent of the 70 million Americans who had tried cannabis described themselves as daily users.


For more than 30 years, the discovery of the mechanism of THC's action had eluded the best researchers. The problem seems finally to have been resolved by the detection of specific cannabinoid-binding sites (Receptors) in the brain. A further step in unraveling the mechanism of THC's action has been the cloning of the cannabinoid receptor.

The pharmacological effects of THC vary with the dose, the method of administration, the user's degree of experience with THC, the setting, and the user's vulnerability to the psychoactive effects of the drug. Most users seek to experience a "high," or "mellowing out." The high begins about 10 to 20 minutes after smoking and lasts about 2 hours. The psychological effects obtained during the high are often related to the setting in which the drug is taken.


THC is most commonly taken into the body by inhaling the smoke from marijuana "joints." A joint of good quality contains about 500 milligrams of marijuana, which in turn contains between 5 and 15 milligrams of THC. Blood levels of THC rise almost as rapidly after inhaling smoke as they do after intravenous administration of THC. That the drug should be so rapidly absorbed is an indication of the efficiency of the lung as a trap for the drug. THC is quickly redistributed into other tissues so that blood levels decline over the course of 3 hours to negligible amounts. The usual symptoms of marijuana intoxication are almost completely gone by that time.


THC is absorbed slowly and unreliably from the gut after oral administration. Blood levels of the drug peak between 1 and 2 hours after ingestion. These peak concentrations are also considerably lower than those following smoking.

THC is easily soluble in fats. It is taken up and stored in the fatty tissues of the body and in the gray matter of the brain. This pattern of storage is one reason why THC remains so long in the body.


THC does not produce a severe withdrawal syndrome. Heavy users, however, frequently report insomnia, nervousness, mild stomach upset, and achy musclesparticularly if they stop their use suddenly.


Drug testing is an issue with respect to marijuana because of the effects of THC on coordination, sense of timing, and impairment of depth perception as well as short-term memory. It is hazardous for someone who has taken a moderate dosage of marijuana to drive or to operate heavy equipment in the workplace.

Urine testing, however, is hardly useful for determining impairment, since the metabolic products of THC are detectable for as long as 50 days in chronic users. Urine tests are also of little use in determining the patient's pattern of use.


THC produces a variety of complex sensations and behavioral effects in humans. The effects on memory, coordination, and sense of time have already been noted. Some studies indicate that THC produces impairment of human cognitive functions as well. In addition, many users experience increased appetite. Psychological effects range from a pleasant sense of mellowness to negative effects that include panic reactions, anxiety, hallucinations, and schizophrenic symptoms. THC can also cause relapses in schizophrenic patients, even those who are taking antipsychotic medications. These negative effects are more common with high doses of the drug and with oral ingestion rather than smoking.

The physical effects of THC include dry mouth, abnormalities in heart rhythm, and abnormal precancerous changes in the tissues that line the airway and the lungs. People who are heavy users of marijuana often develop bronchitis and laryngitis. As of 1999, however, it was not definitely known whether persons who smoke only marijuana have an increased risk of lung cancer, as compared to those who smoke tobacco. THC lowers the sperm count in males and may produce abnormal menstrual cycles in females. Women who are pregnant or nursing are advised to avoid marijuana, as THC is secreted in human breast milk.


THC has been used in medicine to treat the nausea that many cancer patients experience after chemotherapy. It has also been used to prevent convulsions and to lower the fluid pressure inside the eye in treating glaucoma.

In recent years, THC has been replaced in medical use by a synthetic derivative called dronabinol (Marinol). Dronabinol is used as an antinausea drug, an appetite stimulant in AIDS patients, and an antiglaucoma medication.

(See also: Drug Metabolism ; Drug Testing and Analysis ; Pharmacokinetics )


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Leo E. Hollister

Revised by Rebecca J. Frey


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tetrahydrocannabinol (tet-ră-hy-droh-kan-ab-in-ol) n. a derivative of marijuana that has antiemetic activity and also produces euphoria. These two properties are utilized in the prevention of chemotherapy-induced sickness.