Childhood marijuana use can affect brain function and lower IQ: study

A new study out of Western University and the Robarts Research Institute in London, Ontario, has found that childhood marijuana use can detrimentally affect brain functioning and potentially lower IQ.

Researchers were looking into the effects of frequent marijuana use on brain development and mood disorders in youth aged 16 to 23 and found not only that marijuana use did not alleviate depressive symptoms but that it had a deleterious effect on brain functioning in a number of areas related to visuo-spatial processing, memory, self-referential activity and reward processing.

“These findings suggest that using marijuana does not correct the brain abnormalities or symptoms of depression and using it from an early age may have an abnormal effect not only on brain function, but also on IQ,” says Dr. Elizabeth Osuch, of the Lawson Health Research Institute and the Dr. Joseph Rea Chair in Mood Disorders at the Schulich School of Medicine & Dentistry at Western University.

The relationship between marijuana use and both cognitive impairment and mental illness has been the subject of much investigation over the past decade, with growing evidence suggesting a link between marijuana use and the risk of psychiatric disorders ranging from schizophrenia to anxiety and depression. The risks to youth have been a particular focus, including one 11-year study of childhood marijuana users which concluded that early marijuana use was associated with declining educational achievement, lower income, greater unemployment, declining relationship satisfaction and declining life satisfaction.

The current study recruited 74 youth aged 16 to 23 and divided them into four groups depending on both marijuana use (frequent or infrequent) and mood disorder (those with depression and those without). The four groups were put through a range of psychiatric, cognitive and IQ tests, along with brain scans to test for brain functioning.

The study found that perhaps contrary to the perceived wisdom, frequent marijuana use did not correct the brain function deficits associated with depression and in some cases made them worse.

“Many youth in our program use marijuana heavily and, despite past research, believe it improves their psychiatric conditions because it makes them feel better momentarily,” says Dr. Osuch, “For this reason, we decided to study the effects of marijuana and depression on psychiatric symptoms, brain function and cognitive function.”

The research was published in the journal Acta Psychiatrica Scandinavica.

Researchers have recently put another widely assumed attribute of marijuana use to the test, namely, that smoking week improves creativity. The study from Leiden University in the Netherlands found that frequent cannabis users were less capable than others of brainstorming, a process commonly linked to creative performance.

In addition, researchers found that the processes used to monitor one’s activity for mistakes was also negatively affected by cannabis use.

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