Marijuana 

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

are over 200 slang terms for marijuana including "pot," "herb," "weed," "boom," "Mary Jane," "gangster," and "chronic." 

It is usually smoked as a cigarette (called a joint or a nail) or in a pipe or bong. In recent years, marijuana has appeared 

in blunts, which are cigars that have been emptied of tobacco and refilled with marijuana, often in combination with 

another drug, such as crack. Some users also mix marijuana into foods or use it to brew tea. 

The main active chemical in marijuana is THC (delta-9-tetrahydrocannabinol). In 1988, it was discovered that the 

membranes of certain nerve cells contain protein receptors that bind THC. Once securely in place, THC kicks off a 

series of cellular reactions that ultimately lead to the high that users experience when they smoke marijuana. The short 

term effects of marijuana use include problems with memory and learning; distorted perception; difficulty in thinking and 

problem-solving; loss of coordination; and increased heart rate, anxiety, and panic attacks. 

Scientists have found that whether an individual has positive or negative sensations after smoking marijuana can be 

influenced by heredity. A recent study demonstrated that identical male twins were more likely than non-identical male 

twins to report similar responses to marijuana use, indicating a genetic basis for their sensations. Identical twins share 

all of their genes, and fraternal twins share about half. 

Environmental factors such as the availability of marijuana, expectations about how the drug would affect them, the 

influence of friends and social contacts, and other factors that differentiate identical twins' experiences also were found 

to have an important effect; however, it also was discovered that the twins' shared or family environment before age 18 

had no detectable influence on their response to marijuana. 

Health Hazards

Effects of Marijuana on the Brain

Researchers have found that THC changes the way in which sensory information gets into and is processed by the 

hippocampus. The hippocampus is a component of the brain's limbic system that is crucial for learning, memory, and 

the integration of sensory experiences with emotions and motivations. Investigations have shown that neurons in the 

information processing system of the hippocampus and the activity of the nerve fibers in this region are suppressed by 

THC. In addition, researchers have discovered that learned behaviors, which depend on the hippocampus, also 

deteriorate via this mechanism. 

Recent research findings also indicate that long-term use of marijuana produces changes in the brain similar to those 

seen after long-term use of other major drugs of abuse. 

Effects on the Lungs

Someone who smokes marijuana regularly may have many of the same respiratory problems as tobacco smokers. 

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 lung tissue injured or destroyed by marijuana 

smoke. 

Regardless of the THC content, the amount of tar inhaled by marijuana smokers and the level of carbon monoxide 

absorbed are three to five times greater than among tobacco smokers. This may be due to the marijuana users' 

inhaling more deeply and holding the smoke in the lungs and because marijuana smoke is unfiltered. 

Effects on Heart Rate and Blood Pressure

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Recent findings indicate that smoking marijuana while shooting up cocaine has the potential to cause severe increases 

in heart rate and blood pressure. In one study, experienced marijuana and cocaine users were given marijuana alone, 

cocaine alone, and then a combination of both. Each drug alone produced cardiovascular effects; when they were 

combined, the effects were greater and lasted longer. The heart rate of the subjects in the study increased 29 beats per 

minute with marijuana alone and 32 beats per minute with cocaine alone. When the drugs were given together, the 

heart rate increased by 49 beats per minute, and the increased rate persisted for a longer time. The drugs were given 

with the subjects sitting quietly. In normal circumstances, an individual may smoke marijuana and inject cocaine and 

then do something physically stressful that may significantly increase the risk of overloading the cardiovascular system.

Effects of Heavy Marijuana Use on Learning and Social Behavior

A study of college students has shown that critical skills related to attention, memory, and learning are impaired among 

people who use marijuana heavily, even after discontinuing its use for at least 24 hours. Researchers compared 65 

"heavy users," who had smoked marijuana a median of 29 of the past 30 days, and 64 "light users," who had smoked a 

median of 1 of the past 30 days. After a closely monitored 19- to 24-hour period of abstinence from marijuana and other 

illicit drugs and alcohol, the undergraduates were given several standard tests measuring aspects of attention, memory, 

and learning. Compared to the light users, heavy marijuana users made more errors and had more difficulty sustaining 

attention, shifting attention to meet the demands of changes in the environment, and in registering, processing, and 

using information. These findings suggest that the greater impairment among heavy users is likely due to an alteration 

of brain activity produced by marijuana. 

Longitudinal research on marijuana use among young people below college age indicates those who used marijuana 

have lower achievement than the non-users, more acceptance of deviant behavior, more delinquent behavior and 

aggression, greater rebelliousness, poorer relationships with parents, and more associations with delinquent and drugusing friends. 

Research also shows more anger and more regressive behavior (thumb sucking, temper tantrums) in toddlers whose 

parents use marijuana than among the toddlers of non-using parents. 

Effects on Pregnancy

Any drug of abuse can affect a mother's health during pregnancy, making it a time when expectant mothers should take 

special care of themselves. Drugs of abuse may interfere with proper nutrition and rest, which can affect good 

functioning of the immune system. Some studies have found that babies born to mothers who used marijuana during 

pregnancy were smaller than those born to mothers who did not use the drug. In general, smaller babies are more likely 

to develop health problems. 

A nursing mother who uses marijuana passes some of the THC to the baby in her breast milk. Research indicates that 

the use of marijuana by a mother during the first month of breast-feeding can impair the infant's motor development 

(control of muscle movement). 

Addictive Potential

A drug is addicting if it causes compulsive, often uncontrollable drug craving, seeking, and use, even in the face of 

negative health and social consequences. Marijuana meets this criterion. More than 120,000 people enter treatment 

per year for their primary marijuana addiction. In addition, animal studies suggest marijuana causes physical 

dependence, and some people report withdrawal symptoms. 

Extent of Use 

Monitoring the Future Study (MTF) * 

The NIDA-funded MTF provides an annual assessment of drug use among 12th, 10th, and 8th grade students and 

young adults nationwide. After decreasing for over a decade, marijuana use among students began to increase in the 

early 1990s. From 1998 to 1999, use of marijuana at least once (lifetime use) increased among 12th- and 10th-graders, 

continuing the trend seen in recent years. The seniors' rate of lifetime marijuana use is higher than any year since 

1987, but all rates remain well below those seen in the late 1970s and early 1980s. Past year and past month 

marijuana use did not change significantly from 1998 to 1999 in any of the three grades, suggesting the sharp 

increases of recent years may be slowing. Daily marijuana use in the past month increased slightly among all three 

grades as well. 

Percentage of 8th-Graders Who Have Used Marijuana: 

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Monitoring the Future Study, 1999

 

Percentage of 10th-Graders Who Have Used Marijuana: 

Monitoring the Future Study, 1999

 

Percentage of 12th-Graders Who Have Used Marijuana 

Monitoring the Future Study, 1999

 

Community Epidemiology Work Group (CEWG)**

In 1998, marijuana indicators continued an upward trend in most of the 20 CEWG metropolitan areas. Rates of 

emergency department men-tions of marijuana increased significantly in seven sites, with the largest increases 

occurring in Dallas (emergency room mentions increased to 63.9 percent), Boston (to 44.1 percent), Denver (to 40 

percent), San Diego (to 35.1 percent), and Atlanta (to 31.7 percent). The highest percent increase in emergency room 

mentions comparing the first half of 1997 and the first half of 1998 was among 12- to 17-year olds. 

Treatment data for primary abuse of marijuana increased in six CEWG sites and remained stable elsewhere. Marijuana 

treatment admissions were highest in Denver (41 percent of all admissions), Miami (30 percent), New Orleans (22 

percent), and Minneapolis/ St. Paul (20 percent). Half of the treatment admissions for marijuana in Minneapolis/St. Paul 

were under age 18. 

In six of the CEWG sites, juvenile arrestees testing positive for marijuana ranged from a low of 40.3 percent in St. Louis 

to a high of 63.7 percent in Phoenix. More than 50 percent of juvenile arrestees in Los Angeles, Denver, and 

Washington, D.C. tested positive for marijuana, and 48.9 percent in San Diego. Among all arrestees, Seattle was the 

 1991 1992 1993 1994 1995 1996 1997 1998 1999

Ever Used 10.2% 11.2% 12.6% 16.7% 19.9% 23.1% 22.6% 22.2% 22.0%

Used in Past Year 6.2 7.2 9.2 13.0 15.8 18.3 17.7 16.9 16.5

Used in Past Month 3.2 3.7 5.1 7.8 9.1 11.3 10.2 9.7 9.7

Daily Use in Past Month 0.2 0.2 0.4 0.7 0.8 1.5 1.1 1.1 1.4

 1991 1992 1993 1994 1995 1996 1997 1998 1999

Ever Used 23.4% 21.4% 24.4% 30.4% 34.1% 39.8% 42.3% 39.6% 40.9%

Used in Past Year 16.5 15.2 19.2 25.2 28.7 33.6 34.8 31.1 32.1

Used in Past Month 8.7 8.1 10.9 15.8 17.2 20.4 20.5 18.7 19.4

Daily Use in Past Month 0.8 0.8 1.0 2.2 2.8 3.5 3.7 3.6 3.8

 1979 1985 1991 1992 1993 1994 1995 1996 1997 1998 1999

Ever Used 60.4% 54.2% 36.7% 32.6% 35.3% 38.2% 41.7% 44.9% 49.6% 49.1% 49.7%

Used in 

Past Year

 50.8 40.6 23.9 21.9 26.0 30.7 34.7 35.8 38.5 37.5 37.8

Used in 

Past 

Month

 36.5 25.7 13.8 11.9 15.5 19.0 21.2 21.9 23.7 22.8 23.1

Daily Use 

in Past 

Month

 10.3 4.9 2.0 1.9 2.4 3.6 4.6 4.9 5.8 5.6 6.0

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only site where women were more likely than men (37.9 percent vs. 35.4 percent) to test positive for marijuana. 

National Household Survey on Drug Abuse (NHSDA)***

Marijuana remains the most commonly used illicit drug in the United States. There were an estimated 2.1 million people 

who started using marijuana in 1998. According to data from the 1998 NHSDA, more than 72.0 million Americans (33 

percent) 12 years of age and older have tried marijuana at least once in their lifetimes, and almost 18.7 million (8.6 

percent) had used marijuana in the past year. In 1985, 56.5 million Americans (29.4 percent) had tried marijuana at 

least once in their lifetimes, and 26.1 million (13.6 percent) had used marijuana within the past year. 

* MTF is an annual survey on drug use and related attitudes of America's adolescents that began in 1975. The survey 

is conducted by the University of Michigan's Institute for Social Research and is funded by NIDA. Copies of the latest 

survey are available from the National Clearinghouse for Alcohol and Drug Information at 1-800-729-6686.

** CEWG is a NIDA-sponsored network of researchers from 20 major U.S. metropolitan areas and selected foreign 

countries who meet semiannually to discuss the current epidemiology of drug abuse. CEWG's most recent reports are 

available on the CEWG web site.

*** NHSDA is an annual survey conducted by the Substance Abuse and Mental Health Services Administration Copies 

of the latest survey are available from the National Clearinghouse for Alcohol and Drug Information at 1-800-729-6686

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