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National Institute on Drug Abuse -  NIDA NOTES
Volume 11, Number 2
March/April 1996

Facts About Marijuana and Marijuana Abuse


Marijuana is a green, brown, or gray mixture of dried, shredded flowers and leaves of Cannabis sativa, the hemp plant.

Active Ingredient:

Delta-9-tetrahydrocannabinol or THC, one of nearly 400 chemicals in a hemp plant, accounts for most of marijuana's psychoactive, or mind-altering, effects. The strength of the drug is determined by the amount of THC it contains. Recent data show the following:

  • Most ordinary marijuana has an average of 3 percent THC.

  • Sinsemilla, which is made from just the buds and flowering tops of female plants, has an average THC concentration of 7.5 percent, although it can be as high as 24 percent.

  • Hashish, a sticky resin obtained from the female plant flowers, has an average of 2 to 8 percent THC and can contain as much as 20 percent THC.

  • Hash oil, a tar-like liquid distilled from hashish, generally consists of between 15 and 50 percent THC but can have as much as 70 percent THC.

Methods of Use:

Most users roll loose marijuana into a cigarette commonly known as a "joint." A typical joint contains between 0.5 and 1.0 gram of cannabis plant matter, which varies in THC content between 5 and 150 milligrams. The drug also can be smoked in a pipe. One well-known type of water pipe is the bong. Within the past few years, users have found another way to smoke the drug, by slicing open cigars and replacing the tobacco with marijuana. The resulting marijuana cigar is called a "blunt." Some users also mix marijuana into foods or use it to brew tea.

Extent of Use:

Marijuana is the most used illicit drug in the United States. According to the 1994 National Household Survey on Drug Abuse, an average of 10 million Americans use marijuana each month. NIDA's 1995 Monitoring the Future study found that from 1991 to 1995, marijuana use in the 12 months before the surveys rose from 23.9 to 34.7 percent among the Nation's 12th graders, from 16.5 to 28.7 percent among 10th graders, and from 6.2 to 15.8 percent among 8th graders.

Effects of Use:

Within a few minutes of inhaling marijuana smoke, users likely experience dry mouth, rapid heartbeat, some loss of coordination and poor sense of balance, and slower reaction times, along with intoxication. Blood vessels in the eye expand. For some people, marijuana raises blood pressure slightly and can double the normal heart rate. This effect can be greater when other drugs are mixed with marijuana. Research also has documented the following chronic or long-term effects of marijuana use.

Effects on the Brain: THC suppresses the neurons in the information-processing system of the hippocampus, the part of the brain that is crucial for learning, memory, and the integration of sensory experiences with emotions and motivation. Researchers have discovered that learned behaviors, which depend on the hippocampus, deteriorate after chronic exposure to THC. Chronic abuse of marijuana also is associated with impaired attention and memory, while prenatal exposure to marijuana is associated with impaired verbal reasoning and memory in preschool children. Of possible relevance are findings from animal studies showing that chronic exposure to THC damages and destroys nerve cells and causes other pathological changes in the hippocampus.

Effects on the Respiratory System: Someone who smokes marijuana regularly may have many of the same respiratory problems that tobacco smokers have. These individuals may have daily cough and phlegm, symptoms of chronic bronchitis, and more frequent chest colds. Continuing to smoke marijuana can lead to abnormal functioning of the lungs and airways. Scientists have found signs of lung tissue injured or destroyed by marijuana smoke.

NIDA has developed two science-based question-and-answer booklets to educate the public about marijuana. These are Marijuana: Facts for Teens and Marijuana: Facts Parents Need to Know. The Institute also offers a 13-minute informational video for parents called Marijuana: What Can Parents Do? These resources are available from the National Clearinghouse for Alcohol and Drug Information, P.O. Box 2345, Rockville, MD 20847-2345, (800) 729-6686.

From NIDA NOTES, March/April, 1996
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