The Brain’s Response to

Marijuana

Hi, my name’s Sara Bellum. Welcome to my 

magazine series exploring the brain’s response to drugs. In this issue, we’ll investigate the fascinating facts about marijuana. 

Some of this information was 

only recently discovered by 

leading scientists.

You may have heard it called pot, weed, 

grass, ganja or skunk, but marijuana by any 

other name is still a drug that affects the 

brain.

Did you know marijuana can cause some 

people to lose focus on events 

around them? It makes others 

more aware of their physical sensations, and it has still 

more effects on other people.

The Brain’s Response to

Marijuana

Hippocampus

The Search Continues

Some of THC’s effects are useful in the 

world of medicine -- like preventing nausea 

and blocking pain. The trick is for scientists 

to get these results without the harmful 

effects.

Researchers have found out the brain 

makes a chemical -- anandamide -- that 

attaches to the same receptors as THC. This 

discovery may lead to the development of 

medications that are chemically similar 

to THC but less harmful, and they may be 

used for treating nausea and pain.

Mind Over Matter is produced by the National Institute on Drug Abuse, National Institutes 

of Health, U.S. Department of Health and Human Services. These materials are in the public 

domain and may be reproduced without permission. Citation of the source is appreciated. NIH 

Publication No. 06-3859. Printed 1997. Reprinted 1998, 2000, 2003, 2005, 2006.

One region of the brain that contains a lot of THC receptors is the hippocampus, which 

processes memory. When THC attaches to receptors in the hippocampus, it weakens 

short-term memory.

The hippocampus also communicates with other brain regions that process new 

information into long-term memory. (That’s how you can remember today’s math lesson 

or a new friend’s phone number.) In the brain, under the influence of marijuana, new 

information may never register-- and may be lost from memory. 

Maybe you’ve heard that in some people, marijuana can cause uncontrollable laughter 

one minute and paranoia the next. That’s because 

THC also influences emotions, probably by 

acting on a region of the brain called the limbic 

system.

And don’t 

forget this: 

THC can make 

something as 

simple as driving 

a car really 

dangerous.

National Institute on Drug Abuse

National Clearinghouse for Alcohol and Drug Information,

P.O. Box 2345, Rockville, MD 20847

1-800-729-6686

For more information, visit:

www.drugabuse.gov

All these different changes are 

caused by chemicals that affect the 

brain. More than 400 chemicals 

are in the average marijuana plant. 

When smoked, heat produces even 

more of them!
Marijuana is the dried leaves and flowers 

of the hemp plant (Cannabis sativa). Like 

all plants, it’s sensitive to the environment 

where it grows. Different weather and 

soil conditions can change the amounts 

of the chemicals inside the plant. That 

means marijuana grown in a place like 

Hawaii might be chemically stronger than 

marijuana from Mexico, or vice-versa.

Where Does Marijuana Come From?

How do the chemicals in marijuana change 

the way a person sees, hears, smells, tastes, 

and feels things?

When someone uses marijuana, these 

chemicals travel through the bloodstream 

and quickly attach to special places on 

the brain’s nerve cells. These places are 

called receptors, because they receive 

information from other nerve cells and 

from chemicals. When a receptor receives 

information, it causes changes in the nerve 

cell.

The chemical in marijuana that has a 

big impact on the brain is called THC 

-- tetrahydrocannabinol. (Whew! Try 

saying that 10 times fast.) Scientists 

recently discovered that some areas in 

the brain have a lot of THC receptors, 

while others have very few or none. 

These clues are helping researchers 

figure out exactly how THC works in 

the brain.

Marijuana Invades the Brain

Rapid heartbeat -- up to how many 

beats per minute?

Dilated blood vessels -- can be seen 

in what part of the body? 

A feeling of panic -- accompanied by 

what kind of sensations?

Daily cough and more frequent chest 

colds very much like who? 

Marijuana may cause some parts of the body 

to react in different ways. What do you 

remember about:

A

B

C

D

Answers:

A) Marijuana can speed the heart rate up to 160 beats per minute.

B) Dilated blood vessels make the whites of the eyes turn red.

C) Panic feelings may be accompanied by sweating, dry mouth and trouble breathing.

D) Tobacco smokers.

How does marijuana affect nerve cells in the brain? Marijuana causes some parts of the brain --

such as those governing emotions, memory and judgement -- to lose balance and controoooooooooooooooooooooooolllllllll.