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Weed Use

What Happens to Your Brain When You Use Weed for Twenty Years?

By April 2, 2024No Comments

Is Long-Term Weed Use Linked to IQ Loss and Dementia?

A 2022 study led by ASU’s Madeline Meier, Ph.D., suggests that that regular use of marijuana for a long time is linked to two things: a decrease in the size of a part of the brain called the hippocampus, and a decline in how well the brain works. These changes are known to be early signs that someone might develop dementia later in life.

Dr. Meier’s research used data from the Dunedin Longitudinal Study, which surveyed ~1,000 New Zealanders born in 1972 and 1973 at ages 18, 21, 26, 32, 38, and 45. Study participants were interviewed about their substance use and this information was used to identify long-term cannabis users.

Individuals who consistently used marijuana from late adolescence to middle age exhibited more pronounced cognitive deficits compared to non-users. Interestingly, long-term marijuana users showed more cognitive deficits than long-term alcohol or tobacco users.

Long-term weed users saw an average decline in IQ of 5.5 points between adolescence and middle ag, along with decreased learning and processing speed compared to their childhood abilities. Additionally, they reported issues with memory and attention.

By age 45, long-term weed users exhibited hippocampal atrophy, alongside mild cognitive impairments, factors commonly linked to dementia risk.

The hippocampus is a key component of the brain’s limbic system and is primarily responsible for memory formation. Researchers hypothesize that marijuana may lead to structural changes in the hippocampus, such as a decrease in volume or alterations in connectivity between neurons, which can impair its ability to function properly.

About is a free, web-based resource and community created by a team of healthcare professionals and researchers. We distill the facts about marijuana use and its effects into practical guidance for interested persons or for those who are thinking about or struggling to quit weed. Finding reliable, easy to understand information about marijuana should never be a struggle—that is why our core mission is to provide the most up to date information about marijuana use, abuse, addiction, and withdrawal. While we seek to empower individuals to have control over their use, we are not “anti-weed” and we support efforts to legalize adult marijuana use and study.

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