What is marijuana?

Marijuana - often called pot, grass, reefer, weed, herb, mary jane, or mj - is a greenish-gray mixture of the dried, shredded leaves, stems, seeds, and flowers of Cannabis sativa, the hemp plant. Most users smoke marijuana in hand-rolled cigarettes called joints, among other names; some use pipes or water pipes called bongs. Marijuana cigars called blunts have also become popular. To make blunts, users slice open cigars and replace the tobacco with marijuana, often combined with another drug, such as crack cocaine.²¹ Marijuana also is used to brew tea and is sometimes mixed into foods.

The major active chemical in marijuana is delta-9-tetrahydrocannabinol (THC), which causes the mind-altering effects of marijuana intoxication. The amount of THC (which is also the psychoactive ingredient in hashish) determines the potency and, therefore, the effects of marijuana. Between 1980 and 1997, the amount of THC in marijuana available in the United States rose dramatically.²²

What is the scope
of marijuana use
in the United States?

Marijuana is the Nation's most commonly used illicit drug. More than 94 million Americans (40 percent) age 12 and older have tried marijuana at least once, according to the 2003 National Survey on Drug Use and Health (NSDUH).²³

Marijuana use is widespread among adolescents and young adults. The percentage of middle-school students who reported using marijuana increased throughout the early 1990s.²⁴ In the past few years, according to the 2004 Monitoring the Future Survey, an annual survey of drug use among the Nation's middle and high school students, illicit drug use by 8th-, 10th-, and 12th-graders has leveled off.²⁴ Still, in 2004, 16 percent of 8th-graders reported that they had tried marijuana, and 6 percent were current users (defined as having used the drug in the 30 days preceding the survey).²⁴ Among 10th-graders, 35 percent had tried marijuana sometime in their lives, and 16 percent were current users.²⁴ As would be expected, rates of use among 12th-graders were higher still. Forty-six percent had tried marijuana at some time, and 20 percent were current users.²⁴

The Drug Abuse Warning Network (DAWN), a system for monitoring the health impact of drugs, estimated that, in 2002, marijuana was a contributing factor in over 119,000 emergency department (ED) visits in the United States, with about 15 percent of the patients between the ages of 12 and 17, and almost two-thirds male.²⁵

In 2002, the National Institute of Justice's Arrestee Drug Abuse Monitoring (ADAM) Program, which collects data on the number of adult arrestees testing positive for various drugs, found that, on average, 41 percent of adult male arrestees and 27 percent of adult female arrestees tested positive for marijuana.²⁶ On average, 57 percent of juvenile male and 32 percent of juvenile female arrestees tested positive for marijuana.

NIDA's Community Epidemiology Work Group (CEWG), a network of researchers that tracks trends in the nature and patterns of drug use in major U.S. cities, consistently reports that marijuana frequently is combined with other drugs, such as crack cocaine, PCP, formaldehyde, and codeine cough syrup, sometimes without the user being aware of it.²¹ Thus, the risks associated with marijuana use may be compounded by the risks of added drugs, as well.

How does marijuana
affect the brain?

Scientists have learned a great deal about how THC acts in the brain to produce its many effects. When someone smokes marijuana, THC rapidly passes from the lungs into the bloodstream, which carries the chemical to organs throughout the body, including the brain. In the brain, THC connects to specific sites called cannabinoid receptors on nerve cells and thereby influences the activity of those cells. Some brain areas have many cannabinoid receptors; others have few or none. Many cannabinoid receptors are found in the parts of the brain that influence pleasure, memory, thought, concentration, sensory and time perception, and coordinated movement.²⁷