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Marijuana: Facts for Teens

Want to Know More? Some FAQs about Marijuana

A teenage boy sitting in class.

What is marijuana? Are there different kinds?

Marijuana Fact: Most teens 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 sativa, 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 potency, or strength, and therefore its effects. The THC content of marijuana has been increasing over the past few decades (Mehmedic, 2010).

How long does marijuana stay in your body?

Organs in the body have fatty tissues that quickly absorb the THC in marijuana. In general, standard urine tests can detect traces of THC several days after use. In heavy marijuana users, however, urine tests can sometimes detect THC traces for weeks after use stops.

A teenager at her locker.

Does marijuana use lead to other drugs?

Marijuana Fact: Marijuana can be addictive.
About 1 in 6 people who start using as teens and 25 to 50 percent of those who use it every day become addicted.

Long-term studies of drug use patterns show that most high school students who use other illegal drugs have tried marijuana first. 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. For example, animal research suggests that early exposure to marijuana makes opioid 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).

A teenager with his 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 as 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 mixed with other drugs.

In the short-term, marijuana can cause:

  • problems with learning and memory
  • distorted perception (sights, sounds, time, touch)
  • poor coordination
  • increased heart rate

Marijuana affects each person differently according to:

  • biology (e.g., his or her genes)
  • marijuana’s potency
  • previous experience with the drug
  • how the person uses it (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. 

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. Research suggests that the effects on memory, learning, and intelligence can be long term and even permanent in people who begin using marijuana regularly as teens. Lost mental abilities might not fully return even if a person quits using marijuana as an adult (Meier, 2012).

So, while we do know there are differences in the brains of marijuana users versus nonusers, we don't 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 coordination.

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 sellers advertise as both a "safe" and "legal" alternative to that drug. Neither is true. Although the labels on K2/Spice products often claim that they contain "natural" mind-altering material taken from a variety of plants, chemical analyses show that their active ingredients are man-made compounds. Although we don't yet fully know Spice’s effects on the human brain, these compounds act in the same brain areas as THC. However, some chemicals in Spice—often of unknown origin—may produce more powerful and unpredictable effects, like extreme anxiety, paranoia, and hallucinations.

A teenager sitting outside with headphones hanging around his neck.

Can marijuana use by the mother affect a developing fetus or newborn baby?

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. Mothers are also advised not to use marijuana while breastfeeding. Some research suggests that moderate amounts of THC are excreted into breast milk. We don't yet know how this affects a baby’s developing brain.

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, problems sleeping, anxiety, and cravings—peaking a few days after regular marijuana use has stopped. Withdrawal symptoms can make it hard for someone to stay off marijuana.

A teenage girl leaning against a wire 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 patients can use THC and other marijuana ingredients as medicine.

A number of states have passed laws allowing marijuana for medical use, but the Food and Drug Administration (FDA) has not approved the marijuana plant to treat any diseases. Even so, the marijuana plant contains ingredients that could have important medical uses. Currently, the FDA has approved two pill versions of THC 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 patients can use THC and other marijuana ingredients as medicine.

Someone using a mouth spray.

This page was last updated May 2015