Marijuana on the Brain

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The Museum’s Health Sciences Department is partnering with the University of Colorado Anschutz Medical Campus to publish a monthly series on the Museum blog called “Know Health”. The articles focus on current health topics selected by CU’s medical and graduate students in order to provide both English and Spanish speaking communities with current, accurate information. The posts in the “Know Health” series are edited versions of articles that first appeared in Contrapoder magazine. Thank you to the students at the University of Colorado Anschutz Medical Campus for bringing these stories to life.

(aka Dr. Nicole Garneau, chair and curator, Health Sciences Department)

Part I of II: Adolescents

Guest Author, Veronica Searles Quick, is a student at the University of Colorado Anschutz Medical Campus in the School of Medicine.

en español

While opinions may vary on the legalization of marijuana, other countries besides the United States are looking at its medicinal properties and effects. Twenty-three states and Washington, D.C., have legalized marijuana in some form. Four states, including Colorado, have legalized marijuana for recreational use. Given these policy changes, it is important to understand how marijuana affects the brain.

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There are a couple of important things to consider. First, the brain continues to grow and develop well into our teens, and any substance (marijuana, alcohol, cigarettes, etc.) can affect this. Second, there is a lot of “junk science” on the Internet. People publish articles supporting their political opinion that often are not based on strong science.

So what have scientists learned from the studies that have been done, particularly those looking at brain structure, intelligence, and long-term risk for psychiatric disease?

Research that examines brain structure—such as the size of different brain regions—in teenage marijuana users has had inconsistent results, but the research suggests that marijuana induces potentially long-term brain changes. Animal studies support this idea: young mice exposed to marijuana have brain changes that remain once they reach maturity, suggesting an irreversible effect on brain development.

A study from New Zealand found that people who started using marijuana heavily (greater than four times a week for many years) at a young age experienced an eight-point drop in their IQ from age 13 to 38 years. This is a significant drop, especially for teens with developing brains who are approaching early adulthood when there may be negative impacts on success at school and work. This study did not find a drop in IQ if individuals waited until age 18 to start using marijuana, so it appears the greatest damage is done in adolescence, when brain development is more active.

Teens who use marijuana may also be at greater risk of addiction and schizophrenia. This risk is greatest if they start using it at a young age, and use it heavily for long periods of time. But some individuals are less genetically susceptible to this risk; only one in four individuals who use marijuana regularly as teens will go on to develop any type of addiction. Unfortunately, since we do not know who has the risky genes, we do not know who that one will be.

As more states legalize marijuana and use becomes more mainstream, it is even more important to raise awareness about the drug’s effects. For more information, visit or

Editor’s note: The blog post above is an edited version of an original article that first appeared in Contrapoder magazine.

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