Revised

 national institute

on drug abuse national institutes

 of health

Contents...

What is marijuana? 2 

How is marijuana used? 4

How long does marijuana stay in the user’s body? 5

How many teens smoke marijuana? 5

Why do young people use marijuana? 5

What happens if you smoke marijuana? 6

What are the short-term effects of marijuana use? 8

Does marijuana affect school, sports, or other activities? 9

What are the long-term effects of marijuana use? 9

Does marijuana lead to the use of other drugs? 10

How can you tell if someone has been using marijuana? 11

Is marijuana sometimes used as a medicine? 11

How does marijuana affect driving? 12

If a woman is pregnant and smokes marijuana,

will it hurt the baby? 12

What does marijuana do to the brain? 14

Can people become addicted to marijuana? 14

What if a person wants to quit using the drug? 16

/ 1.
Q: What is marijuana?

Aren’t there different kinds?

A: Marijuana is a green, brown, or gray mixture of dried, shredded 

leaves, stems, seeds, and flowers of the hemp plant. You may 

hear marijuana called by street names such as pot, herb, weed, 

grass, boom, Mary Jane, gangster, or chronic. There are more 

than 200 slang terms for marijuana.

 Sinsemilla (sin-seh-me-yah; it’s a Spanish word), 

hashish (“hash” for short), and hash oil are stronger forms 

of marijuana.

 All forms of marijuana are mind-altering. In other 

words, they change how the brain works. They all contain THC 

(delta-9-tetrahydrocannabinol), the main active chemical in 

marijuana. They also contain more than 400 other chemicals. 

Marijuana’s effects on the user depend on its strength or 

potency, which is related to the amount of THC it contains. 

The THC content of marijuana has been increasing since 

the 1970s. 

/ 2.
Most teenagers do 

not use marijuana.

Fewer than one in

four high school

seniors is a current 

marijuana user.
/ 4.

Q: How is marijuana used?

A: Marijuana is usually smoked as a cigarette (called a joint or 

a nail) or in a pipe or a bong. Recently, it has appeared in 

cigar wrappers called blunts, when it is often combined with 

another drug, such as crack cocaine.

“I don’t think it’s 

cool at all and I 

don’t see why they 

try to pressure it 

on other people.”

 — from the videotape, 

Marijuana: What Can 

Parents Do?
Q: How long does marijuana stay

in the user’s body?

A: THC in marijuana is rapidly 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 chronic heavy users, 

traces can sometimes be detected for weeks after they have 

stopped using marijuana.

Q: How many teens smoke marijuana?

A: Contrary to popular belief, most teenagers do not use 

marijuana. Among students surveyed in a yearly national 

survey, only about one in six 10th graders report they are 

current marijuana users (that is, used marijuana within the 

past month). Fewer than one in four high school seniors 

is a current marijuana user.

Q: Why do young people use marijuana?

A: There are many reasons why some children and young teens 

start smoking marijuana. Many young people smoke marijuana 

because they see their brothers, sisters, friends, or even 

older family members using it. Some use marijuana because 

of peer pressure. 

 Others may think it’s cool to use marijuana because 

they hear songs about it and see it on TV and in movies. Some 

/ 5.
/ 6.

teens may feel they need marijuana and other drugs to help 

them escape from problems at home, at school, or with friends.

 No matter how many shirts and caps you see printed 

with the marijuana leaf, or how many groups sing about it, 

remember this: You don’t have to use marijuana just because 

you think everybody else is doing it. Most teenagers do not 

use marijuana. 

Q: What happens if you smoke marijuana?

A: The way the drug affects each person depends on many 

factors, including:

 • user’s previous experience with the drug;

 • how strong the marijuana is (how much THC it has);

 • what the user expects to happen;

 • where the drug is used; 

 • how it is taken; and

 • whether the user is drinking alcohol or using 

other drugs.

 Some people feel nothing at all when they smoke 

marijuana. Others may feel relaxed or high. Sometimes 

marijuana makes users feel thirsty and very hungry—

an effect called “the munchies.”

 Some users can undergo bad effects from marijuana. 

They may suffer sudden feelings of anxiety and have paranoid 

thoughts. This is more likely to happen when a more potent 

variety of marijuana is used.
Marijuana can mess 

up your performance 

in school, sports,

and other parts of 

your life.
Q: What are the short-term effects of 

marijuana use?

A: The short-term effects of marijuana include:

 • problems with memory and learning;

 • distorted perception (sights, sounds, time, touch);

 • trouble with thinking and problemsolving;

 • loss of motor coordination; and

 • increased heart rate.

/ 8.

“I used to be 

real athletic. 

When I started 

using drugs, I

just stopped playing all together 

‘cause I thought I 

had more important 

things to do.”

 — from the videotape, 

Marijuana: What Can 

Parents Do?
 These effects are even greater when other drugs are mixed 

with the marijuana; and users do not always know what 

drugs are given to them.

Q: Does marijuana affect 

school, sports, or other activities?

A: It can. Marijuana affects memory, judgment and perception. 

 The drug can make you mess up in school, in sports or clubs, 

or with your friends. If you’re high on marijuana, you are more 

likely to make mistakes that could embarrass or even hurt 

you. If you use marijuana a lot, you could start to lose 

interest in how you look and how you’re getting along at 

school or work. 

 Athletes could find their performance is off; timing, 

movements, and coordination are all affected by THC. Also, 

since marijuana can affect judgment and decisionmaking, 

its use can lead to risky sexual behavior, resulting in exposure to sexually transmitted diseases like HIV, the virus that 

causes AIDS.

Q: What are the long-term 

effects of marijuana use?

A: Findings so far show that regular use of marijuana may play 

a role in some kinds of cancer and in problems with the 

respiratory and immune systems.

• Cancer—It’s hard to know for sure whether regular marijuana 

use causes cancer. But it is known that marijuana contains 

/ 9.
some of the same, and sometimes even more, of the cancercausing chemicals found in tobacco smoke. 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.

• Lungs and airways—People who smoke marijuana often 

develop the same kinds of breathing problems that cigarette 

smokers have: coughing and wheezing. They tend to have 

more chest colds than nonusers. They are also at greater

risk of getting lung infections like pneumonia.

• Immune system—Animal studies have found that THC can 

damage the cells and tissues in the body that help protect 

against disease. When your immune cells are weakened, you 

are more likely to get sick. 

Q: Does marijuana lead to

the use of other drugs?

A: It could. Long-term studies of high school students and 

 their patterns of drug use show that very few young people 

 use other illegal drugs without first trying marijuana. For 

 example, the risk of using cocaine is much greater for those 

 who have tried marijuana than for those who have never 

 tried it. Using marijuana puts children and teens in contact 

 with people who are users and sellers of other drugs. So 

 there is more of a risk that a marijuana user will be exposed 

 to and urged to try more drugs.

/ 10.
/ 11.

 To better determine this risk, scientists 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. Further research is needed to predict who will 

be at greatest risk.

Q: How can you tell if someone

has been using marijuana?

A: 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.

Q: Is marijuana sometimes

used as a medicine?

A: There has been much talk 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. 

 THC, the active chemical in marijuana, is manufactured 

into a pill available by prescription that can be used to treat 
/ 12.

the nausea and vomiting that occur with certain cancer treatments and to help AIDS patients eat more to keep up their 

weight. According to scientists, more research needs to be 

done on THC’s side effects and other potential medical uses.

Q: How does marijuana affect driving?

A: Marijuana has serious harmful effects on the skills required 

to drive safely: alertness, concentration, coordination, and 

reaction time. Marijuana use can make it difficult to judge 

distances and react to signals and sounds on the road.

 Marijuana may play a role in car accidents. 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. Data 

have also shown 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.

Q: If a woman is pregnant and smokes

marijuana, will it hurt the baby?

A: Doctors advise pregnant women not to use any drugs because 

they could harm the growing fetus. Although one animal study 

linked marijuana use to loss of the fetus very early in 

pregnancy, two studies in humans found no association 
Marijuana and 

driving do not 

mix. Users often 

have delayed 

responses to 

sights and

sounds drivers 

need to notice.
/ 14.

between marijuana use and early pregnancy loss. More 

research is necessary to fully understand the effects of 

marijuana use on pregnancy outcomes.

 Studies in children born to mothers who use marijuana 

have shown increased behavioral problems during infancy and 

preschool years. In school, these children are more likely to 

have problems with decisionmaking, memory, and the ability 

to remain attentive.

 Researchers are not certain whether health problems 

that may be caused by early exposure to marijuana will 

remain as the child grows into adulthood. However, since 

some parts of the brain continue to develop throughout 

adolescence, it is also possible that certain kinds of problems 

may appear as the child matures.

Q: What does marijuana do to the brain? 

A: Some studies show that when people have smoked large 

amounts of marijuana for years, the drug takes its toll on 

mental functions. Heavy or daily use of marijuana affects

 the parts of the brain that control memory, attention, and 

learning. A working short-term memory is needed to learn 

and perform tasks that call for more than one or two steps.

 Smoking marijuana causes some changes in the brain

that are like those caused by cocaine, heroin, and alcohol.
“When I would sit 

down and try to 

figure something 

out it was like 

my brain would 

stop working.”

 — from the videotape, 

Marijuana: What Can 

Parents Do?

 Scientists are still learning about the many ways that marijuana can affect the brain.

Q: Can people become addicted

to marijuana?

A: Yes. Long-term marijuana use can lead to addiction in some 

people. That is, they cannot control their urges to seek out 

and use marijuana, even though it negatively affects their 

family relationships, school performance, and recreational 

activities. According to one study, marijuana use by teenagers 

who have prior antisocial problems can quickly lead to addiction. In addition, some frequent, heavy marijuana users 

/ 15.
develop “tolerance” to its effects. This means they need larger and larger amounts of marijuana to get the same desired 

effects as they used to get from smaller amounts.

Q: What if a person wants to

quit using the drug?

A: In 2002, over 280,000 people entering drug treatment programs reported marijuana as their primary drug of abuse. 

However, up until a few years ago, it was hard to find treatment programs specifically for marijuana users. 

 Now researchers are testing different ways to help 

marijuana users abstain from drug use. There are currently 

no medications for treating marijuana addiction. Treatment 

programs focus on counseling and group support systems. 

There are also a number of programs designed especially

 to help teenagers who are abusers. Family doctors can be 

a good source for information and help in dealing with 

adolescent marijuana problems.

/ 16.
For more information on marijuana

and other drugs, visit the National

Institute on Drug Abuse Web site

at www.drugabuse.gov,

www.marijuana-info.org, or

www.teens.drugabuse.gov

and/or contact:

National Clearinghouse for

Alcohol and Drug Information

P.O. Box 2345

Rockville, MD 20847

1-800-729-6686

(The TDD number is

1-800-487-4889.)

This publication may be 

reprinted without permission.
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

NIH Publication No. 04-4037

Printed 1995, Revised November 1998

Reprinted April 2001, Revised March 2003

Revised September 2004