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

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.