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Marijuana affects both the cardiovascular and central nervous systems. The major psychoactive component in marijuana is delta-9-tetrahydrocannabinol, or THC. After entering the bloodstream through blood-gas exchanges associated with smoking, THC combines with receptor sites in the human brain to cause drowsiness, increased appetite, giddiness, hallucinations, and other psychoactive effects. Although the causative mechanisms are not fully known, current research indicates that THC ingestion results in THC binding to receptor sites associated with measurable memory loss. Other studies correlate THC binding to receptors in the cerebellum and correlated decreases in motor coordination and/or the ability to maintain balance. At low doses there tends to be a sense of well-being, drowsiness, and relaxation. As the dose increases, other effects take place such as an altered sense of time and sensory awareness, difficulty in balancing and remembering from one moment to another (short-term memory). Conversation and thoughts become incomplete, and exaggerated laughter may take place with increased doses. At higher doses, severe psychological disturbances can take place such as paranoia, hallucinations, panic attacks, and the acting out of delusions.

The cardiovascular system is affected by an increased heart rate and dilation of eye blood vessels. The American Heart Association maintains that marijuana smoking may induce heart attacks. Difficulty in coordinating body movements and pains in the chest may be other effects of the drug. Heavy users may experience a decrease in immune function. Males who smoke marijuana could also experience a decreased sperm count. Less is known about marijuana's effects on the lungs than cigarette smoking, but the evidence points to long-term damage similar to the effects of tobacco smoking. Chronic users suffer from throat irritation, persistent cough, chronic bronchitis, and emphysema.

The FDA, in 1985, gave approval for the use of two psychoactive chemicals from marijuana to prevent nausea and vomiting after chemotherapy in cancer treatment. THC can be prescribed in capsule form for these patients. Research suggests that compounds, other than THC, inhaled when smoking marijuana can also be used for medicinal purposes. Marijuana may help stop the weight loss in AIDS patients, it might lower eye pressure in people with glaucoma, it may control spasms in multiple sclerosis patients, and it could be used to relieve chronic pain.

See also Addiction.



Grinspoon, Lester, and James B. Bakalar. The Forbidden Medicine. New Haven: Yale University Press, 1993.

Shapiro, Harry. Waiting for the Man. New York: William Morrow, 1988.

Stimmel, Barry. The Facts About Drug Use. New York: Haworth Medical Press, 1991.


Bakalar, James B. "The War on Drugs: a Peace Proposal." The New England Journal of Medicine (Feb 3 1994): 357-61.

Jordan P. Richman



—Psychoactive compounds found in the marijuana plant.

Cannabis sativa

—The botanical name for the hemp (marijuana) plant.


—The Unites States Federal Drug Administration; oversees and regulates the introduction of new drug products into the medical marketplace.

"Gateway" drug

—Theory of drug enforcers who argue that even if Marijuana is not in the same class as certain narcotics, it should be treated the same way because it introduces people, especially the young, to those "harder" drugs.


—An eye disease that seems to be helped by the main psychoactive compound in marijuana.


—A more potent form of marijuana that comes from the flower part of the plant.

Jazz Age

—The period from the 1920s to the early 1930s, which saw the introduction of marijuana and other drugs through the music of that period.


—A group of drugs (opiates) that depress or decrease the activity of the central nervous system. Two effects of narcotics is that they give relief from pain and produce a state of euphoria. They also have a high potential for addiction.


—The 18th amendment, which prohibited the use and sale of alcohol in the 1920s and was repealed in the early 1930s. Marijuana use spread as a substitute for alcohol.

Psychoactive drugs

—Drugs which contain chemicals that affect the mind or behavior.

Tetrahydrocannabinol (THC)

—The main psychoactive compound in marijuana.

Additional topics

Science EncyclopediaScience & Philosophy: Macrofauna to MathematicsMarijuana - History, Effects