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Teenage Marijuana Use Affects Brain Development

Heavy teenage marijuana use could damage brain structures critical to memory and reasoning and the effects may be long lasting. Heavy pot use during teenage years is also connected with lower IQ.  It is well known that the human brain is not fully developed until 25-28 years of age.  Chronic or heavy pot use by teenagers may affect the brain as it develops, perhaps permanently.  A number of interesting recent studies look at marijuana use by teens and the possible effects it has on brain development.

Marijuana and Memory

According to new research by Northwestern Medicine, the brains of heavy marijuana teen users were altered in regions that involve memory and reasoning. Young people with such alterations performed worse on memory tests than the non-using control subjects, despite the fact that the heavy users had not used marijuana for more than two years, on average, before the testing.

The study looked at MRI brain scans of several areas of the brain.  Heavy pot users showed greater brain abnormalities than those who had not used marijuana. The researchers found that memory-related brain structures appeared to shrink and collapse inward. These findings could indicate long-term detriments to chronic marijuana use during the teen years.

Although this study doesn’t prove causation, it does provide evidence of a need for caution.  It also showed that the earlier or younger the pot use began, the greater the brain’s abnormalities.

Mental Illness and Marijuana Connection

In June 2013, an Australian study showed that prolonged use of cannabis or marijuana by young adults was linked to a higher risk of developing psychosis.  The highest risk was for those who started using the substance in their teens, and continued using it for 6 years or more into adulthood. For this group, the risk of developing psychosis was more than double that of those who never used marijuana.

Marijuana and Dopamine

A recent study by Imperial College London revealed that long-term use of cannabis depletes dopamine, the feel-good chemical in the brain that inspires a spirit of get-up-and-go.  The study found greater dopamine depletion if marijuana use was heavier and if the first initial use was at an earlier age.

Marijuana and IQ

A long term study in New Zealand indicates that early and long term marijuana use may cause IQ to decrease.  The study measured IQ prior to age 13 and then surveyed over 1000 participants from a single city born in the same year over a period of decades.  According to the study, IQ decreased an average of 7-8 points by age 38 for those who used marijuana heavily at some point in the 25 years between ages 13 and 38, with greater decreases in IQ for those with longer periods of heavy marijuana use.


All of the studies show correlations and not actual direct cause.  However, we are seeing that heavy marijuana use in teens could be creating possible lasting changes in the brain.  The earlier heavy use begins, the greater the changes to the brain.

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Written By: New Hope Recovery Center

Want more information about marijuana or young adults and addiction? Check out our Journal for related articles or see below: 

Marijuana Warning Signs: Is Your Teen Smoking Weed? Are you concerned your teenager or young adult is using marijuana? Below you will find the warning signs and symptoms for marijuana use. Marijuana use is very controversial across the nation, but something that cannot be denied, is the detrimental effect it has on young adults. It has been proven that young adults/teenagers who use marijuana have more problems with memory, attention and learning. They also struggle with their school performance, have an increased risk of problematic behaviors, and are more likely to suffer from depression and or anxiety.

Marijuana and Addiction Treatment All too often people enter treatment for addiction from a variety of substances with the belief that marijuana is not a drug.  “Alcohol is my problem, not marijuana” or “Marijuana is not addictive” – the list of justifications people use could fill an entire page.  We have all heard the term “gateway drug” in reference to marijuana but often the thought process is that this occurs early in the stages of addiction. However, we have seen that marijuana can be a gateway drug at any point in addiction or recovery.

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