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Addiction and Substance Abuse

Cannabis and Brain



I am from Greece.I`ve been a regular user of cannabis for four years now,but I have reduced smoking a lot since last summer.I would like to know if my IQ and all cognitive functions of my brain have been affected negatively in the four year period I`ve been a user, even if the impairment is subtle.If your answer is yes, the loss is permanent or cognition returns to the initial point after cessation of use? (I am deeply sorry if my english is not good)


I cannot know for certain whether or not cannabis has negatively affected your cognitive functions and IQ. This would depend on many other factors, such as the age at which you started using, your genetic makeup, the environment in which you were raised, and other drugs or toxins that you may have been exposed to (example: alcohol, lead, etc.)

A recent review entitled "Long-term effects of exposure to cannabis" by Leslie Iverson (a pharmacologist) was published in February 2005 in Current Opinion in Pharmacology (5:69-72).

According to the article, heavy marijuana use (at least 5000 uses in a lifetime) caused lower scores on a battery of psychological tests for 1 week after stopping use. However, there were no differences between heavy users and controls by day 28 (that is, 28 days with no cannabis).

Other studies reviewed in this article showed mixed evidence; some studies showed no long-term effects on neuropsychological functioning, while other studies reported subtle impairments in the ability to learn and remember new information.

In general, cannabis may predispose individuals to psychotic illnesses (like schizophrenia), long term lung damage, as well as cognitive deficits. Whether or not these cognitive deficits are permanent is still not conclusively known.


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Response by:

Christina M Delos Reyes, MD Christina M Delos Reyes, MD
Assistant Professor of Psychiatry
School of Medicine
Case Western Reserve University