Marijuana: Facts Parents Need to Know

What is Marijuana? Are there different kinds?

Marijuana is a green, brown, or gray mixture of dried, shredded leaves, stems, seeds, and flowers of the hemp plant (Cannabis sativa). Before the 1960s, many Americans had never heard of marijuana, but today it is the most often used illegal drug in this country.

Cannabis is a term that refers to marijuana and other drugs made from the same plant. Strong forms of cannabis include sinse-milla (sin-seh-me-yah), hashish (“hash” for short), and hash oil.

All forms of cannabis are mind-altering (psychoactive) drugs; they all contain THC (delta-9-tetrahydrocannabinol), the main active chemical in marijuana. They also contain more than 400 other chemicals.

Marijuana’s effect on the user depends on the strength or potency of the THC it contains (6) . THC potency has increased since the 1970s but has been about the same since the mid-1980s. The strength of the drug is measured by the average amount of THC in test samples confiscated by law enforcement agencies.

  • Most ordinary marijuana has an average of 3 percent THC.
  • Sinsemilla (made from just the buds and flowering tops of female plants) has an average of 7.5 percent THC, with a range as high as 24 percent.
  • Hashish (the sticky resin from the female plant flowers) has an average of 3.6 percent, with a range as high as 28 percent.
  • Hash oil, a tar-like liquid distilled from hashish, has an average of 16 percent, with a range as high as 43 percent.


There are stronger forms of marijuana available to adolescents today than in the 1960s. Stronger marijuana means stronger effects.

What are the current slang terms for marijuana?

There are many different names for marijuana. Slang terms for drugs change quickly, and they vary from one part of the country to another. They may even differ across sections of a large city.

Terms from years ago, such as pot, herb, grass, weed, Mary Jane, and reefer, are still used. You might also hear the names Aunt Mary, skunk, boom, gangster, kif, or ganja.

There are also street names for different strains or “brands” of marijuana, such as ” Texas tea,” ” Maui wowie,” and “Chronic.” A recent book of American slang lists more than 200 terms for various kinds of marijuana.

How is marijuana used?

Most users roll loose marijuana into a cigarette (called a joint or a nail) or smoke it in a pipe. One well-known type of water pipe is the bong. Some users mix marijuana into foods or use it to brew a tea. Another method is to slice open a cigar and replace the tobacco with marijuana, making what’s called a blunt. When the blunt is smoked with a 40 oz. bottle of malt liquor, it is called a “B-40.”

Lately, marijuana cigarettes or blunts often include crack cocaine, a combination known by various street names, such as “primos” or “woolies.” Joints and blunts often are dipped in PCP and are called “happy sticks,” “wicky sticks,” “love boat,” or “tical.”

How many people smoke marijuana? At what age do children generally start?

A recent government survey tells us:

  • Marijuana is the most frequently used illegal drug in the United States . Over 83 million Americans over the age of 12 have tried marijuana at least once.
  • Over 12 million had used the drug in the month before the survey.

The Monitoring the Future Survey, which is conducted yearly, includes students from 8th, 10th, and 12th grades. In 2001, the survey showed that 20 percent of 8th-graders have tried marijuana at least once, and by 10th grade, 20 percent are “current” users (that is, used within the past month) (19) . Among 12th-graders, nearly 50 percent have tried marijuana/hash at least once, and about 22 percent were current users (19) .

Other researchers have found that use of marijuana and other drugs usually peaks in the late teens and early twenties, then declines in later years.


Research shows that nearly 50 percent of teenagers try marijuana before they graduate from high school.

How can I tell if my child has been using marijuana?

There are some signs you might be able to see. If someone is high on marijuana, he or she might

  • seem dizzy and have trouble walking;
  • seem silly and giggly for no reason;
  • have very red, bloodshot eyes; and
  • have a hard time remembering things that just happened.

When the early effects fade, over a few hours, the user can become very sleepy.

Parents should be aware of changes in their child’s behavior, although this may be difficult with teenagers. Parents should look for withdrawal, depression, fatigue, carelessness with grooming, hostility, and deteriorating relationships with family members and friends. In addition, changes in academic performance, increased absenteeism or truancy, lost interest in sports or other favorite activities, and changes in eating or sleeping habits could be related to drug use. However, these signs may also indicate problems other than use of drugs.

In addition, parents should be aware of:

  • signs of drugs and drug paraphernalia, including pipes and rolling papers.
  • odor on clothes and in the bedroom
  • use of incense and other deodorizers
  • use of eye drops
  • clothing, posters, jewelry, etc., promoting drug use

Why do young people use marijuana?

Children and young teens start using marijuana for many reasons. Curiosity and the desire to fit into a social group are common reasons. Certainly, youngsters who have already begun to smoke cigarettes and/or use alcohol are at high risk for marijuana use.

Also, our research suggests that the use of alcohol and drugs by other family members plays a strong role in whether children start using drugs. Parents, grandparents, and older brothers and sisters in the home are models for children to follow.

Some young people who take drugs do not get along with their parents. Some have a network of friends who use drugs and urge them to do the same (peer pressure). All aspects of a child’s environment – home, school, neighborhood – help to determine whether the child will try drugs.

Children who become more heavily involved with marijuana can become dependent, and that is their prime reason for using the drug. Others mention psychological coping as a reason for their use – to deal with anxiety, anger, depression, boredom, and so forth. But marijuana use is not an effective method for coping with life’s problems, and staying high can be a way of simply not dealing with the problems and challenges of growing up.

Researchers have found that children and teens (both male and female) who are physically and sexually abused are at greater risk than other young people of using marijuana and other drugs and of beginning drug use at an early age (7) .

Does using marijuana lead to other drugs?

Long-term studies of high school students and their patterns of drug use show that very few young people use other drugs without first trying marijuana, alcohol, or tobacco. Though few young people use cocaine, for example, the risk of doing so is much greater for youth who have tried marijuana than for those who have never tried it (9) . While research has not fully explained this association, growing evidence suggests a combination of biological, social, and psychological factors are involved.

Researchers are examining the possibility that long-term marijuana use may create changes in the brain that make a person more at risk of becoming addicted to other drugs, such as alcohol or cocaine (16) . While many young people who use marijuana do not go on to use other drugs, further research is needed to determine who will be at greatest risk.

What are the effects of marijuana?

The effects of marijuana on each person depend on the

  • type of cannabis and how much THC it contains;
  • way the drug is taken (by smoking or eating);
  • experience and expectations of the user;
  • setting where the drug is used; and
  • whether drinking or other drug use is also going on.

Some people feel nothing at all when they first try marijuana. Others may feel high (intoxicated and/or euphoric).

It’s common for marijuana users to become engrossed with ordinary sights, sounds, or tastes, and trivial events may seem extremely interesting or funny. Time seems to pass very slowly, so minutes feel like hours. Sometimes the drug causes users to feel thirsty and very hungry-an effect called “the munchies.”

What happens after a person smokes marijuana?

Within a few minutes of inhaling marijuana smoke, the user will likely feel, along with intoxication, a dry mouth, rapid heartbeat, some loss of coordination and poor sense of balance, and slower reaction time. Blood vessels in the eye expand, so the user’s eyes look red.

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; but users do not always know when that happens.

As the immediate effects fade, usually after 2 to 3 hours, the user may become sleepy.

How long does marijuana stay in the user’s body?

THC in marijuana is readily absorbed by fatty tissues in various organs. Generally, traces (metabolites) of THC can be detected by standard urine testing methods several days after a smoking session. However, in heavy, chronic users, traces can sometimes be detected for weeks after they have stopped using marijuana.

Can a user have a bad reaction?

Yes. Some users, especially someone new to the drug or in a strange setting, may suffer acute anxiety and have paranoid thoughts. This is more likely to happen with high doses of THC. These scary feelings will fade as the drug’s effects wear off.

In rare cases, a user who has taken a very high dose of the drug can have severe psychotic symptoms and need emergency medical treatment.

Other kinds of bad reactions can occur when marijuana is mixed with other drugs, such as PCP or cocaine.

How is marijuana harmful?

Marijuana can be harmful in a number of ways, through both immediate effects and damage to health over time.

Marijuana hinders the user’s short-term memory (memory for recent events), and he or she may have trouble handling complex tasks. With the use of more potent varieties of marijuana, even simple tasks can be difficult.

Because of the drug’s effects on perceptions and reaction time, users could be involved in auto crashes. Drug users also may become involved in risky sexual behavior. There is a strong link between drug use and unsafe sex and the spread of HIV, the virus that causes AIDS.

Under the influence of marijuana, students may find it hard to study and learn (14) . Young athletes could find their performance is off; timing, movements, and coordination are all affected by THC.

Some of the more long-range effects of marijuana use are described later in this document.


Marijuana has adverse effects on many of the skills for driving a car. Driving while high leads to car accidents.

How does marijuana affect driving?

Marijuana affects many skills required for safe driving: alertness, the ability to concentrate, coordination, and reaction time. These effects can last up to 24 hours after smoking marijuana. Marijuana use can make it difficult to judge distances and react to signals and sounds on the road.

There are data showing that marijuana can play a role in crashes. When users combine marijuana with alcohol, as they often do, the hazards of driving can be more severe than with either drug alone.

A study of patients in a shock-trauma unit who had been in traffic accidents revealed that 15 percent of those who had been driving a car or motorcycle had been smoking marijuana, and another 17 percent had both THC and alcohol in their blood (17) .

In one study conducted in Memphis , TN , researchers found that, of 150 reckless drivers who were tested for drugs at the arrest scene, 33 percent tested positive for marijuana, and 12 percent tested positive for both marijuana and cocaine (2) . Data also show that while smoking marijuana, people show the same lack of coordination on standard “drunk driver” tests as do people who have had too much to drink (11) .


Marijuana users may have many of the same respiratory problems that tobacco smokers have, such as chronic bronchitis and inflamed sinuses.

What are the long-term effects of marijuana?

While all of the long-term effects of marijuana use are not yet known, there are studies showing serious health concerns. For example, a group of scientists in California examined the health status of 450 daily smokers of marijuana but not tobacco. They found that the marijuana smokers had more sick days and more doctor visits for respiratory problems and other types of illness than did a similar group who did not smoke either substance (13) .

Findings so far show that the regular use of marijuana or THC may play a role in cancer and problems in the respiratory, and immune systems.


It is hard to find out whether marijuana alone causes cancer because many people who smoke marijuana also smoke cigarettes and use other drugs. Marijuana smoke contains some of the same cancer-causing compounds as tobacco, sometimes in higher concentrations. Studies show that someone who smokes five joints per day may be taking in as many cancer-causing chemicals as someone who smokes a full pack of cigarettes every day (20) .

Tobacco smoke and marijuana smoke may work together to change the tissues lining the respiratory tract. Marijuana smoking could contribute to early development of head and neck cancer in some people.

Immune system

Our immune system protects the body from many agents that cause disease. It is not certain whether marijuana damages the immune system of people. But both animal and human studies have shown that marijuana impairs the ability of T-cells in the lungs’ immune defense system to fight off some infections.

Lungs and Airways

People who smoke marijuana regularly may develop many of the same breathing problems that tobacco smokers have, such as daily cough and phlegm production, more frequent chest colds, a heightened risk of lung infections, and a greater tendency toward obstructed airways. Cancer of the respiratory tract and lungs may also be promoted by marijuana smoke, since it contains irritants and carcinogens. Marijuana smokers usually inhale more deeply and hold their breath longer, which increases the lungs’ exposure to carcinogenic smoke. Thus, puff for puff, smoking marijuana may increase the risk of cancer more than smoking tobacco does.

What about pregnancy: Will smoking marijuana hurt the baby?

Doctors advise pregnant women not to use any drugs because they might harm the growing fetus. One animal study has linked marijuana use to loss of the fetus very early in pregnancy.

Some scientific studies have found that babies born to women who used marijuana during their pregnancy display altered responses to visual stimulation, increased tremors, and a high pitched cry, which may indicate problems with nervous system development. During pre- and early school years, marijuana-exposed children have been reported to have more behavioral problems and difficulties with sustained attention and memory than nonexposed children (3) .

Researchers are not certain whether any effects of marijuana during pregnancy persist as the child grows up; however, because some parts of the brain continue to develop into adolescence, it is also possible that certain kinds of problems will become more evident as the child matures.

What happens if a nursing mother uses marijuana?

When a nursing mother uses marijuana, some of the THC is passed to the baby in her breast milk. This is a matter for concern, since the THC in the mother’s milk is much more concentrated than that in the mother’s blood. One study has shown that the use of marijuana by a mother during the first month of breastfeeding can impair the infant’s motor development (control of muscle movement) (15) .


Marijuana smoking affects the brain and leads to impaired short-term memory, perception, judgment and motor skills.

How does marijuana affect the brain?

THC affects the nerve cells in the part of the brain where memories are formed. This makes it hard for the user to recall recent events (such as what happened a few minutes ago). It is hard to learn while high – a working short-term memory is required for learning and performing tasks that call for more than one or two steps.

Among a group of long-time heavy marijuana users in Costa Rica , researchers found that the people had great trouble when asked to recall a short list of words (a standard test of memory). People in that study group also found it very hard to focus their attention on the tests given to them (5) .

As people age, they normally lose nerve cells in a region of the brain that is important for remembering events. Chronic exposure to THC may hasten the age-related loss of these nerve cells. In one study, researchers found that rats exposed to THC every day for 8 months (about 1/3 of their lifespan), showed a loss of brain cells comparable to rats that were twice their age. It is not known whether a similar effect occurs in humans. Researchers are still learning about the many ways that marijuana could affect the brain.

Can the drug cause mental illness?

Scientists do not yet know how the use of marijuana relates to mental illness. Among the difficulties in this kind of research are determining whether drug use precedes or follows mental health problems; whether one causes the other; and/or whether both are due to other factors such as genetics or environmental conditions. High doses of marijuana can induce psychosis (disturbed perceptions and thoughts), and marijuana use can worsen psychotic symptoms in people who have schizophrenia. There is also evidence of increased rates of depression, anxiety, and suicidal thinking in chronic marijuana users. However, it is not yet clear whether marijuana is being used in an attempt to self-medicate an already present but otherwise untreated mental health problem, or whether marijuana use leads to mental disorders (or both).

Do marijuana users lose their motivation?

Some frequent, long-term marijuana users show signs of a lack of motivation (amotivational syndrome). Their problems include not caring about what happens in their lives, no desire to work regularly, fatigue, and a lack of concern about how they look. As a result of these symptoms, some users tend to perform poorly in school or at work. Scientists are still studying these problems.

Can a person become addicted to marijuana?

Yes. While not everyone who uses marijuana becomes addicted, when a user begins to seek out and take the drug compulsively, that person is said to be dependent on the drug or addicted to it. In 1999, over 220,000 people entering drug treatment programs reported marijuana as their primary drug of abuse, showing they needed help to stop using (12) .

Some heavy users of marijuana show signs of dependence because when they do not use the drug, they develop withdrawal symptoms. Some subjects in an experiment on marijuana withdrawal had symptoms, such as restlessness, loss of appetite, trouble sleeping, weight loss, and shaky hands.

According to one study, marijuana use by teenagers who have prior serious antisocial problems can quickly lead to dependence on the drug. That study also found that, for troubled teenagers using tobacco, alcohol, and marijuana, progression from their first use of marijuana to regular use was about as rapid as their progression to regular tobacco use, and more rapid than the progression to regular use of alcohol (4) .

What is “tolerance” for marijuana?

“Tolerance” means that the user needs increasingly larger doses of the drug to get the same desired results that he or she previously got from smaller amounts. Some frequent, heavy users of marijuana may develop tolerance for it.

Are there treatments to help marijuana users?

Up until a few years ago, it was hard to find treatment programs specifically for marijuana users. Treatments for marijuana dependence were much the same as therapies for other drug abuse problems. These include behavioral therapies, such as cognitive behavioral therapy; multi systemic therapy; individual and group counseling; and regular attendance at meetings of support groups such as Narcotics Anonymous.

Recently, researchers have been testing different ways to attract marijuana users to treatment and help them abstain from drug use. There are currently no medications for treating marijuana dependence. Treatment programs focus on counseling and group support systems. From these studies, drug treatment professionals are learning what characteristics of users are predictors of success in treatment and which approaches to treatment can be most helpful.

Further progress in treatment to help marijuana users includes a number of programs set up to help adolescents in particular. Some of these programs are in university research centers, where most of the young clients report marijuana as their drug of choice. Others are in independent adolescent treatment facilities. Family physicians are also a good source for information and help in dealing with adolescents’ marijuana problems.

Can marijuana be used as medicine?

There has been much debate in the media about the possible medical use of marijuana. Under U.S. law since 1970, marijuana has been a Schedule I controlled substance. This means that the drug, at least in its smoked form, has no commonly accepted medical use.

In considering possible medical uses of marijuana, it is important to distinguish between whole marijuana and pure THC or other specific chemicals derived from cannabis. Whole marijuana contains hundreds of chemicals, some of which are clearly harmful to health.

THC, manufactured into a pill that is taken by mouth, not smoked, can be used for treating the nausea and vomiting that go along with certain cancer treatments and is available by prescription. Another chemical related to THC (nabilone) has also been approved by the Food and Drug Administration for treating cancer patients who suffer nausea. The oral THC is also used to help AIDS patients eat more to keep up their weight.

Scientists are studying whether marijuana, THC, and related chemicals in marijuana (called cannabinoids) may have other medical uses. According to scientists, more research needs to be done on marijuana’s side effects and potential benefits before it can be recommended for medical use.

How can I prevent my child from getting involved with marijuana?

There is no magic bullet for preventing teenage drug use. But parents can be influential by talking to their children about the dangers of using marijuana and other drugs, and remain actively engaged in their children’s lives. Even after teenage children enter high school, parents can stay involved in schoolwork, recreation, and social activities with their children’s friends. Research shows that appropriate parental monitoring can reduce future drug use, even among those adolescents who may be prone to marijuana use, such as those who are rebellious, cannot control their emotions, and experience internal distress. To address the issue of drug abuse in your area, it is important to get involved in drug abuse prevention programs in your community or your child’s school. Find out what prevention programs you and your children can participate in together.

Talking to your children about marijuana

As shown, marijuana is clearly a dangerous drug which poses a particular threat to the health and well-being of children and adolescents at a critical point in their lives – when they are growing, learning, maturing, and laying the foundation for their adult years. As a parent, your children look to you for help and guidance in working out problems and in making decisions, including the decision not to use drugs. As a role model, your decision to not use marijuana and other illegal drugs will reinforce your message to your children.

There are numerous resources, many right in your own community, where you can obtain information so that you can talk to your children about drugs. To find these resources, you can consult your local library, school, or community service organization.

The National Clearinghouse for Alcohol and Drug Information (NCADI) offers an extensive collection of publications, videotapes, and educational materials to help parents talk to their children about drug use. For more information on marijuana and other drugs, contact:

National Clearinghouse for Alcohol and Drug Information (NCADI)
P.O. Box 2345
Rockville , MD 20847
(TDD Number 1-800-487-4889)


Center for Substance Abuse Prevention, U.S. Department of Health and Human Services. Keeping Youth Drug Free: A Guide for Parents, Grandparents, Elders, Mentors, and Others Caregivers. NCADI Stock No. PHD711, 1996.

Harrison, P.A.; Fullerson, J.A.; and Beebe, T.J. Multiple substance use among adolescent physical and sexual abuse victims. Child Abuse and Neglect 21(6):529-539, 1997.

Hermes, W.J., and Galperin, A. The Encyclopedia of Psychoactive Drugs: Marijuana, Its Effects on Mind and Body. Chelsea House Publishers, 1992.

National Institute on Drug Abuse. Marijuana: Facts Parents Need to Know. NIH Publication No. 95-4036, 1995.

National Institute on Drug Abuse. Marijuana: Facts for Teens. NIH Publication No. 95-4037, 1995.

National Institute on Drug Abuse. Marijuana: What Can Parents Do?, Videotape. NCADI Stock No. VHS82, 1995, cost $12.50.

National Institute on Drug Abuse. Preventing Drug Use Among Children and Adolescents: A Research-Based Guide. NIH Publication No. 97-5212, March 1997.

Substance Abuse and Mental Health Services Administration, Office of Applied Sciences. Preliminary Results From the 1996 National Household Survey on Drug Abuse. DHHS No. (SMA) 97-3149. Rockville , MD : SAMHSA, July 1997.

Substance Abuse and Mental Health Services Administration, Office of Applied Sciences. National Household Survey on Drug Abuse Main Findings 1996. DHHS No. (SMA) 98-3200. Rockville , MD :SAMHSA, April 1998.

U.S. Department of Education. Growing Up Drug Free: A Parent’s Guide to Prevention, Washington , D.C. : NCADI Publication No. PHD533, 1993. (Note: This item is out of stock but can be viewed on the NCADI Web site at

University of Michigan . News and Information Services. Drug use among American teens shows signs of leveling after a long rise. December 18, 1997 .


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Source: The National Institute on Drug Abuse (NIDA)
Updated March 18, 2003

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