Marijuana and the Developing Brain

The brain is the most complex organ in the human body, and scientists continue to learn about how it develops and functions. One growing area of research is about the effects of marijuana on the developing teenage brain.

More research is needed in this area, but studies to date show marijuana use has risks and may impact young people’s mental health. Youth need to know about these risks so that they can make an informed choice.

  • Early marijuana use may lead to a smaller brain, with less gray matter.

    One study quoted by the CCSA reported that long term marijuana users who began using before the age of 17, had smaller brains. Users also had a lower percentage of gray matter, which is the part of the brain that is responsible for processing.

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  • Early marijuana use impacts psychological functions like “visual scanning skills,” which help us to find relevant information in our surroundings. This can impact driving and academics.

    Research quoted by the Canadian Centre on Substance Abuse (CCSA) shows that people who begin using marijuana at an early age, may be more prone to subtle long-term brain deficits than those who begin use later in life. According to CCSA, visual scanning is a psychological function that has a major maturing process around 12-15 years of age. Visual scanning is the ability to quickly find relevant information in our surroundings. Research has shown that early on-set marijuana users (before age 16), showed decreased visual scanning skills. This can affect everything from driving to academic achievement.

  • Marijuana use can change the brain chemistry that controls mood, which can lead to depression and anxiety.

    The links between marijuana use and depression are widely debated. A lot of research concludes that the same factors (genetic, environmental, and social) that can cause depression, can also lead to marijuana use. Recent studies show that heavy marijuana use and depression occur together very often. This has led some researchers to explore the idea that marijuana use may actually cause depression, especially in youth.

  • Marijuana use changes the amount of the chemical dopamine in the brain, which is linked to psychotic disorders like schizophrenia. Young people may be more at risk because their brains are still developing.

    According to CCSA, psychotic disorders (like schizophrenia), involve changes in dopamine, a chemical in the brain. Cannabinoids, such as THC found in marijuana, are linked with more release of dopamine. This may be why frequent marijuana users are found to have a greater risk of having a psychotic outcome. The link between marijuana use and psychosis seems to be stronger in people who are already at risk for psychosis (e.g. family history). It’s not known for sure if the age when someone first uses marijuana affects the risk of developing psychosis. Some studies have seen a link, while others have not. According to the CCSA, the effects of marijuana may be greater in those who use it early in their youth because their developing brains are prone to changes. Teen users may also be at greater risk because they tend to smoke marijuana more often.

In this video Dr. Ken C. Winters (Director of the Center for Adolescent Substance Abuse Research at the University of Minnesota) educates viewers on the vulnerability of the adolescent and teen developing brain as well as the detrimental effects of drugs and alcohol
A short animated video about the effects of cannabis on the brain. Brain development, adolescence and short and long-term effects of cannabis/weed/pot are explained in simple language. Supported by the Australian Government.


Frances E. Jensen, MD, senior assistant in Neurology at Children’s Hospital Boston and a professor at Harvard Medical School, is translating the most up-to-date research on the teen brain which she shares with parents, teachers and teens during her presentation, “Teen Brain 101.”

The teenage brain is not just an adult brain with fewer miles on it. It is a paradoxical time of development. These are people with very sharp brains, but they’re not quite sure what to do with them.

Frances E. Jensen, Professor of Neurology – Children’s Hospital Boston and Harvard Medical School.

The Teenage Brain - Part 1

The Teenage Brain - Part 2

The Teenage Brain - Part 3

Marijuana and the Developing Brain

In 2010 David Suzuki’s show called “The Nature of Things” aired an episode on CBC-TV titled “The Downside of High”. 

See the program.
Marijuana and the Developing Brain

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