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Effects of Marijuana on the Adolescent Brain

Key points:

  • While marijuana is legal in some states, research shows that it can be dangerous to young people because the brain does not fully develop until the age of 25.

  • Studies have shown that heavy marijuana use in adolescence can cause physical changes to the brain, memory and learning issues, decreased driving ability, and poorer quality of life.


With the legalization of marijuana in some places across the country, it’s understandable to think that this substance is safe. But years of research shows that marijuana use may be harmful to adolescents and their developing brains.

Teenager struggling with marijuana use, and brain efffects

How does marijuana affect adolescents’ brains?

The human brain doesn’t fully develop until the age of 25, making adolescents who frequently smoke marijuana and THC (tetrahydrocannabinol) – the psychoactive ingredient in cannabis – more sensitive to its adverse health effects. Some of these health risks include:

  • Physical changes to the brain: Researchers discovered that heavy marijuana use may damage the brain’s white matter and decrease gray matter. As a result of these physical changes, you may find it hard to control yourself, make decisions, and learn.

  • Decreased attention, memory and IQ: The THC in marijuana attaches to the receptors in your brain responsible for focus and making new memories. It may be harder to remember what you recently saw or heard, especially in the hours or days after using marijuana. Your school performance could also be affected. A landmark study found that heavy marijuana consumption caused a roughly six-point drop in IQ from childhood to adulthood.

  • Impaired driving ability: Because marijuana impairs your impulses and coordination, it may also impact your driving ability. Driving while under the influence of marijuana can double your risk of a car accident. Marijuana users are also more likely to drive above the speed limit and speed through red lights.

  • Risk of addiction and poor quality of life: Heavy marijuana use at an early age may negatively impact your life trajectory. If you use before the age of 18, you could be four to seven times more likely to develop a marijuana use disorder. Other studies correlate marijuana use with higher school dropout rates, unemployment, and overall dissatisfaction with life.

Distracted teen student

Overall, more education about the risks of marijuana use is needed in schools and among youth and their families. If you think your child is abusing marijuana, talk to your pediatrician. You can also contact the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-HELP (4357) for support.

By Kristin Erekson Barton, MA, CHES

Reviewed by Cindy Bistany, DHSc

Full Text With Citations of Effects of M
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