Revised

    national institute

on drug abuse      national institutes

          of health

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

NIH Publication No. 10-4037

Printed 1995, Revised November 1998

Reprinted April 2001, Revised March 2003,

September 2004, March 2008, March 2011
Did you know that marijuana 

use among U.S. teens has dropped dramatically since 

the late 1990s? So...if you were thinking everyone smokes pot, 

they don’t. Statistics show that about 15 percent, or roughly 

1 in 7 teens, report past-month marijuana use. In the last few 

years, however, the decline in marijuana use has stalled, and 

the reason may be that fewer of you consider marijuana to be 

a harmful drug. 

BUT...that perception is not correct. In 2009, among 

marijuana users 12 and older, 4.3 million had a marijuana 

abuse or addiction problem, according to clinical diagnostic 

criteria. Look inside this booklet to see what else we know, 

because marijuana is not as harmless as you may think. 

Our goal is to give you the straight facts, so you can make 

smart choices and be your best self—without drugs. And 

we hope you will continue the conversation and share this 

information with your peers, parents, teachers, and others. 

Letter to Teens

You can find treatment

programs through this Web site

www.findtreatment.samhsa.gov

provided by the Substance Abuse

and Mental Health Services

Administration (SAMHSA).

Also, you can call the SAMHSA

Treatment Referral hotline at

1-800-662-HELP. Treatment can

help you, a friend, or someone

you love get back to the person

you or they once were.

Need

Treatment?

Nora D. Volkow, M.D.

Director

National Institute on Drug Abuse
/ 1.

Letter to Teens

I. Some Things to Think About 3

Addiction 3

Driving 4

School 4

Psychosis/Panic 5

II. Want to Know More? 

Some FAQs About Marijuana 6

What is marijuana? Are there different kinds? 6 

How does marijuana exert its effects? 6

How long does marijuana stay in your body? 8

Does marijuana use lead to other drugs? 10

What happens if you smoke marijuana? 10

What are the activities/behaviors most likely to be affected? 12

What does marijuana do to the brain? 12

How does smoking marijuana affect the lungs? 14

Can marijuana affect the developing fetus? 16

Does marijuana produce withdrawal symptoms

when someone quits using it? 16

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

Isn’t marijuana sometimes used as a medicine? 18

III. Other Useful Resources 20

Contents...
/ 2. / 3.

ADDICTION:

Marijuana is addictive. Of course, not everyone who smokes 

marijuana will become addicted—that depends on a whole 

bunch of factors—including your family history (genes), the 

age you start using, whether you also use other drugs, family 

and peer relationships, success in school, etc. Repeated 

marijuana use can lead to addiction—which means that 

people have difficulty controlling their drug use and often 

cannot stop even though they want to, and even though 

it undermines many aspects of their lives. Research shows 

that approximately 9 percent, or about 1 in 11, of those 

who use marijuana at least once will become addicted. This 

rate increases to 16 percent, or about 1 in 6, if you start in 

your teens, and goes up to 25–50 percent among daily users. 

Moreover, among young people in drug abuse treatment, 

marijuana accounts for the largest percentage of admissions: 

61 percent of those under age 15 and 56 percent of those 

15–19.

People smoke pot for a lot of 

different reasons: to feel good, to 

feel better, to feel different, or to 

fit in. Whatever the reason, drug 

use has consequences.

To help you make an 

informed choice, the following are some brief 

summaries of what marijuana research is telling 

us. These topics represent the most popular 

questions and comments we get every day 

on our teen Web site and blog. Share them 

with your friends to help them separate 

fact from myth. This booklet also includes 

FAQs and additional resources for more 

information.

I. Some Things to Think About
/ 4. / 5.

DRIVING: 

Marijuana is UNsafe if you are behind the wheel. Marijuana 

is the most common illegal drug found in drivers who die in 

accidents (around 14 percent of drivers), often in combination 

with alcohol or other drugs. Marijuana affects a number of 

skills required for safe driving—alertness, concentration, 

coordination, and reaction time—so it’s not safe to drive high 

or to ride with someone who’s been smoking. Marijuana makes 

it hard to judge distances and react to signals and sounds on 

the road. And combining marijuana with drinking even a small 

amount of alcohol greatly increases driving danger, more than 

either drug alone. 

SCHOOL: 

Marijuana is linked to school failure. Marijuana’s negative 

effects on attention, memory, and learning can last for 

days and sometimes weeks—especially if you smoke often. 

Someone who smokes marijuana daily may be functioning with 

a ‘dimmed-down’ brain most or all of the time. Compared with 

their peers who don’t smoke, students who smoke marijuana 

tend to get lower grades and are more likely to drop out of 

high school. Also, longtime marijuana users themselves report 

being less satisfied with their lives, experiencing memory and 

relationship problems, poorer mental and physical health, 

lower salaries, and less career success.

PSYCHOSIS/PANIC: 

High doses of marijuana can cause psychosis or panic 

when you’re high. Some people experience an acute 

psychotic reaction (disturbed perceptions and thoughts, 

paranoia) or panic attacks while under the influence of 

marijuana. This usually goes away as the drug’s effects wear 

off. Scientists do not yet know if marijuana use causes lasting 

mental illness, although it can worsen psychotic symptoms 

in people who already have the mental illness schizophrenia, 

and it can increase the risk of long-lasting psychosis in those 

vulnerable to the disease.
/ 6. / 7.

Q: What is marijuana? 

Are there different kinds?

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

leaves, stems, seeds, and flowers of the hemp, or cannabis, 

plant. It goes by many different names—pot, herb, weed, 

grass—and stronger forms include sinsemilla (sin-sehme-yah), hashish (“hash” for short), and hash oil.

Q: How does marijuana exert its effects?

A: All forms of marijuana are mind-altering (psychoactive). In 

other words, they change how the brain works. Marijuana 

contains more than 400 chemicals, including THC (delta-9-

tetrahydrocannabinol). Since THC is the main active chemical 

in marijuana, the amount of THC in marijuana determines its 

strength or potency and therefore its effects. The THC content 

of marijuana has been increasing since the 1980s.

Most teenagers do 

not use marijuana.

II. Want to Know More?

Some FAQs About Marijuana
/ 8. / 9.

“I used 

to smoke pot until 

I had an anxiety attack and thought 

I couldn’t breathe...I was wheezing, 

and I got really paranoid.”

“There are a million things to do 

that are more fun than smoking 

some unknown grass. Go to the 

beach, go to the movies, go to 

the gym—you are not missing 

anything.”

—Comments submitted to NIDA's Sara Bellum Blog

Marijuana is 

addictive. About 

1 in 6 people who 

start using as a 

teen, and 25–50 

percent of those who 

use it every day, 

become addicted to 

marijuana.

Q: How long does marijuana stay in 

your body?

A: The THC in marijuana is rapidly absorbed by fatty tissues in 

various organs throughout the body. In general, standard 

urine tests can detect traces (metabolites) of THC several 

days after use. In heavy users, however, THC metabolites can 

sometimes be detected for weeks after use stops.
/ 10. / 11.

Q: Does marijuana use lead to 

other drugs?

A: Long-term studies of drug use patterns show that very few 

high school students use other illegal drugs without first 

trying marijuana. However, many young people who use 

marijuana do not go on to use other drugs. Among those who 

do, here are some theories: 

•	 Exposure to marijuana may affect the brain, particularly 

during development, which continues into the early 

twenties. Effects may include changes to the brain 

that make other drugs more appealing. Animal research 

supports this possibility—that early exposure to cannabis 

makes opiate drugs more rewarding, for example.

•	 Someone who is using marijuana may be in contact with 

other users as well as sellers of other drugs, increasing 

the risk of being encouraged or tempted to try them.

•	 People at high risk of using drugs may use marijuana 

first because of its availability (probably cigarettes and 

alcohol, too). 

Q: What happens if you smoke marijuana?

A: Some people feel nothing at all when they smoke marijuana. 

Others may feel relaxed or high. Some experience sudden 

feelings of anxiety and paranoid thoughts (more likely with 

stronger varieties of marijuana). Regular use of marijuana 

has also been associated with depression, anxiety, and an 

amotivational syndrome, which means a loss of drive or 

ambition, even for previously rewarding activities. Marijuana 

also often makes users feel hungry. Its effects can be 

unpredictable, especially when other drugs are mixed with it.

In the short-term, marijuana can cause:

•	 problems with learning and memory;

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

•	 diminished motor coordination; and

•	 increased heart rate.

But marijuana affects each person differently according to:

•	 biology (e.g., his or her genes);

•	 marijuana’s strength or potency (how much THC it has);

•	 the circumstances of its use and expectations of effects;

•	 previous experience with the drug;

•	 how it’s taken (smoked versus ingested); and

•	 whether alcohol or other drugs are involved.

“I was lazy a lot. 

I didn’t want to do things... I 

was depressed. I felt like I was 

always in a rut. I was always 

feeling bad about myself, where 

I was standing in life.”

 —from Alby’s story, on his experiences with 

being a daily marijuana smoker.
/ 12. / 13.

Q: What are the activities/behaviors 

most likely to be affected?

A: Learning: Marijuana’s effects on attention and memory 

make it difficult not only to learn something new, but to do 

complex tasks that require focus and concentration or the 

stringing together of a lot of information sequentially.

Sports: Marijuana affects timing, movement, and 

coordination, which can throw off athletic performance.

Judgment: Marijuana, like most abused substances, can 

alter judgment and reduce inhibitions. This can lead to risky 

behaviors that can expose the user to sexually transmitted 

diseases like HIV, the virus that causes AIDS.

Q: What does marijuana do to the brain? 

A: We know a lot about where marijuana acts in the brain and 

how it exerts its effects at specific sites called cannabinoid 

receptors. These are found in brain regions that influence 

learning and memory, appetite, coordination, and pleasure. 

That’s why marijuana produces the effects it does. We know 

much less about what happens to the brain in the long run, 

when someone is a regular marijuana smoker. 

 Scientists use brain imaging techniques to study the 

living human brain, but we are still in the early stages of that 

research when it comes to marijuana. So, while differences 

show up in the brains of marijuana users (versus nonusers), 

Marijuana and driving 

do not mix. It is the 

most common illegal 

drug found in drivers 

who die in accidents 

(around 14 percent of 

drivers), sometimes 

in combination with 

alcohol or other drugs.
/ 14. / 15.

we do not yet know what these differences mean or how long 

they last—especially if someone stops using the drug. One 

reason is that it’s hard to find marijuana-only smokers who do 

not also abuse alcohol—which has its own negative effects 

on brain function.

Q: How does smoking marijuana affect 

the lungs?

A: Someone who smokes marijuana regularly may have many of 

the same respiratory problems that tobacco smokers do, such 

as daily cough, more frequent upper respiratory illnesses, 

and a greater risk of lung infections like pneumonia. As with 

tobacco smoke, marijuana smoke consists of a toxic mixture 

of gases and tiny particles, many of which are known to harm 

the lungs. Although we don’t yet know if marijuana causes 

lung cancer, many people who smoke marijuana also smoke 

cigarettes, which do cause cancer—and smoking marijuana 

can make it harder to quit tobacco use. 

Marijuana affects 

the brain—altering 

memory, judgment, 

and motor skills.
/ 16. / 17.

Q: Can marijuana affect the developing 

fetus?

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

they could harm the growing fetus. Studies suggest that 

children of mothers who used marijuana while pregnant may 

have subtle brain changes that can cause difficulties with 

problemsolving skills, memory, and attention. More research 

is needed because it is hard to say for sure what causes what: 

for example, pregnant women who use marijuana may also 

smoke cigarettes or drink alcohol, both of which can also 

affect fetal development.

Q: Does marijuana produce 

withdrawal symptoms when 

someone quits using it? 

A: Yes. The symptoms are similar in type and severity to those of 

nicotine withdrawal—irritability, sleeping difficulties, anxiety, 

and craving—peaking a few days after marijuana use has 

stopped. Withdrawal symptoms can make it hard for someone 

to stay off marijuana. 

Q: What if a person wants to quit using 

the drug?

A: Researchers are testing different ways to help marijuana users 

abstain from drug use, including developing medications. 

Current treatment programs focus on counseling and group 

support systems. There are also a number of programs 

designed especially to help teenagers.

TJONES1—

JUNCTION CITY HIGH 

SCHOOL, OREGON:

If you’re dating someone 

who does marijuana, does 

that increase your chance 

of doing it? 

NIDA:

Great question! 

Research shows that individuals who have 

friends who use drugs are more likely 

to use drugs themselves. But, we don't 

really know why this is the case. It 

could be that, by hanging out with drug 

users, you have more opportunities to 

try drugs. Certainly, you can choose not 

to try drugs if offered—but this can 

be a challenge. An alternative approach 

would be to see if your friend will 

stop using marijuana—for your benefit 

and his/hers.

—from NIDA’s 2009 CHAT DAY
/ 18. / 19.

Q: Isn’t marijuana sometimes used as a 

medicine?

A: Several states have passed medical marijuana laws, but 

marijuana has not been approved by the Food and Drug 

Administration (FDA) to treat any diseases. Even so, we know 

that the marijuana plant contains ingredients that could have 

important medical uses. Currently, two pill versions of THC, 

marijuana’s psychoactive ingredient, have been approved 

to treat nausea in cancer chemotherapy patients and to 

stimulate appetite in some patients with AIDS. Also, a new 

product called Sativex is available in the United Kingdom and 

Canada as a mouth spray. It is a chemically pure mixture of 

plant-derived THC and cannabidiol (another chemical found 

in the marijuana plant) approved to relieve cancer-associated 

pain and spasticity and nerve pain in multiple sclerosis. 

However, it’s important to remember that because marijuana 

is usually smoked and has ingredients that can vary from 

plant to plant, the associated health risks may outweigh its 

value as a treatment. Scientists continue to investigate the 

medicinal properties of THC and other manmade or plantderived cannabinoids to better evaluate and harness their 

potential to alleviate suffering, while avoiding the harmful 

effects of smoking marijuana, including addiction.

Among youth receiving 

substance abuse 

treatment, marijuana 

accounts for the 

largest percentage of 

admissions: 61 percent 

of those under 15, and 

56 percent of those 

15–19.
/ 20.

Here are some helpful 

places to go for more information:

This publication may be reprinted without permission.

The NIDA Web site www.drugabuse.gov has information 

on a variety of drugs and related topics. NIDA’s teen site 

www.teens.drugabuse.gov covers a lot of ground, with 

free downloads, entertaining and informative videos and 

games, and our Sara Bellum blog for teens, where you can 

even leave us a comment or two. Get the scoop on how 

different drugs affect the brain and body, and read real 

stories from teens who have struggled with drug abuse 

and addiction. 

To learn more about mental health disorders like 

depression or schizophrenia, visit the National Institute 

of Mental Health at www.nimh.nih.gov and read the 

Director’s Blog on various topics that include suicide 

prevention, bipolar and borderline personality disorders, 

coping with traumatic events, and more.

The National Institute on Alcohol Abuse and Alcoholism 

Web site www.niaaa.nih.gov contains the latest research, 

news, and other resources related to alcohol. They even 

have a site especially for young teens called “the cool 

spot” http://www.thecoolspot.gov/, with quizzes and 

other interactive screens that give you information on 

alcohol and resisting peer pressure.

III. Other Useful Resources