En español

Marijuana: Facts for Teens

Want to Know More?- Some FAQs about Marijuana

Image of teenager

What is marijuana? Are there different kinds?

Marijuana Fact: Most teenagers do not use marijuana.

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-seh-me-yah), hashish (“hash” for short), and hash oil.

"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 blog for teens

How does marijuana work?

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. 

How long does marijuana stay in your body?

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. 

Image of a girl at her locker

Does marijuana use lead to other drugs?

Marijuana Fact: 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.

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. To explain why some do, here are a few theories: 

  • Exposure to marijuana may affect the brain, particularly during development, which continues into the early 20s. Effects may include changes to the brain that make other drugs more appealing. Animal research supports this possibility—for example, early exposure to marijuana makes opiate drugs (like Vicodin or heroin) more pleasurable. 
  • Someone who is using marijuana is likely to be in contact with other users and 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 it is easy to get (like cigarettes and alcohol).

Image of a teenager with a skateboard.

What happens if you smoke marijuana?

"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.

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 (even more likely with stronger varieties of marijuana). Regular use of marijuana has also been linked to depression, anxiety, and a loss of drive or motivation, which means a loss of interest even in previously enjoyable activities. 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)
  • poor motor coordination
  • 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)
  • previous experience with the drug
  • how it's taken (smoked versus ingested)
  • whether alcohol or other drugs are involved

How is marijuana likely to affect you?

Learning: Marijuana’s effects on attention and memory make it difficult to learn something new or do complex tasks that require focus and concentration. 

Sports: Marijuana affects timing, movement, and coordination, which can harm athletic performance. 

Judgment: Marijuana, like most abused substances, can alter judgment. This can lead to risky behaviors that can expose the user to sexually transmitted diseases like HIV, the virus that causes AIDS. 

Image of two teenage girls playing soccer.

What does marijuana do to the brain?

We know a lot about where marijuana acts in the brain and how it affects specific sites called cannabinoid receptors. These receptors 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 we do know there are differences in the brains of marijuana users (versus nonusers), 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 people who only smoke marijuana without using alcohol, which has its own negative effects on the brain.

Marijuana Fact: Marijuana affects the brain—altering memory, judgment, and motor skills.

How does smoking marijuana affect the lungs?

Someone who smokes marijuana regularly may have many of the same breathing and lung problems that tobacco smokers do, such as a daily cough, and a greater risk of lung infections like pneumonia. As with tobacco smoke, marijuana smoke has a toxic mixture of gases and tiny particles that can 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 cigarette smoking. 

What is K2/Spice and how does it affect the brain? 

The chemicals in many products sold as K2/Spice are unknown. Some varieties could cause dramatically different effects than the user might expect.

K2/Spice refers to a wide variety of chemical-coated herbal mixtures that have effects similar to marijuana and that are often sold as both a "safe" and a "legal" alternative to that drug—neither is true. Although the labels on K2/Spice products often claim that they contain “natural” psychoactive material taken from a variety of plants, chemical analyses show that their active ingredients are synthetic compounds, made artificially. Although we do not yet fully know Spice’s effects on the human brain, these compounds act in the same brain areas as THC, the main ingredient in marijuana. However, some chemicals in Spice—often of unknown origin—may produce more powerful and unpredictable effects, like extreme anxiety, paranoia, and hallucinations.

Image of a teenage boy sitting in a playground lot.

Can marijuana affect the developing fetus?

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 people 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 chances to try drugs. Certainly, you can choose not to try drugs if offered—but this can be a challenge. Another approach would be to see if your friend will stop using marijuana—for your benefit and his/hers. 

— from NIDA's  CHAT DAY

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 problem-solving 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 the baby's development. 

Does marijuana produce withdrawal symptoms when someone quits using it?

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 regular marijuana use has stopped. Withdrawal symptoms can make it hard for someone to stay off marijuana. 

Image of teenage girl leaning against a fence.

What if a person wants to quit using marijuana?

Researchers are testing different ways to help marijuana users stay off the drug, including some medications. Current treatment programs focus on counseling and group support systems. There are also a number of programs designed especially to help teenagers.

Isn't marijuana sometimes used as a medicine?

Marijuana Fact: Scientists continue to investigate safe ways that THC and other marijuana ingredients can be used as medicine.

Several states have passed laws allowing marijuana for medical use, 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 that is a chemically controlled mixture of THC and cannabidiol (another chemical found in the marijuana plant) is available in several countries outside the United States as a mouth spray. However, it’s important to remember that because marijuana is usually smoked into the lungs and has ingredients that can vary from plant to plant, its health risks may outweigh its value as a treatment. Scientists continue to investigate safe ways that THC and other marijuana ingredients can be used as medicine. 

Image of someone using a mouth spray.

This page was last updated July 2013