White Matter Levels Are Similar in Cannabis Users and People with Schizophrenia

Reductions in white brain matter have been linked to cognitive impairments. Decreased white matter is one symptom of schizophrenia and has also been found in people who are at risk for psychosis. This same symptom has also been discovered in individuals with long-term cannabis use. However, little research has examined whether or not extensive cannabis use increases the risk for psychotic symptoms, or if schizophrenic individuals who use cannabis experience poorer cognitive functioning than those who do not use cannabis. In an attempt to address this gap, N. Solowij of the School of Psychology at the University of Wollongong in Australia conducted a study looking at how white brain matter varied in different classifications of individuals. Solowij recruited 15 cannabis users without schizophrenia, 8 with schizophrenia, 9 individuals with schizophrenia alone, and 16 healthy, nonusing individuals.

Solowij analyzed the participants using magnetic resonance imaging scans (MRIs) and discovered that the healthy individuals who used cannabis had a 23.9% reduction in white brain matter compared to those who did not. Additionally, cannabis users who also had schizophrenia had 29.7% less white brain matter than those who did not use. Because decreased white brain matter is linked to impaired cognitive functioning and reasoning, the results suggest that individuals who use cannabis could become vulnerable to psychotic-type symptoms. Further, for individuals with schizophrenia, using cannabis could increase symptom severity and duration. Overall, the findings of the study imply that people with long-term cannabis use have significantly less white brain matter than individuals with schizophrenia who do not use cannabis. Solowij also pointed out that individuals with schizophrenia, specifically those who develop it in early adulthood, may actually change the course of their brain maturation by using cannabis. Clinicians treating individuals with schizophrenia should consider exploring their clients’ cannabis use in order to better understand and manage the severity of their symptoms in relation to their illness.

Solowij, N., Yucel, M., Respondek, C., Whittle, S., Lindsay, E., Pantelis, C., Lubman, D. I. Cerebellar White-Matter Changes in Cannabis Users With and Without Schizophrenia. Psychological Medicine 41.11 (2011): 2349-359. Print.

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  • Hardy B

    Hardy B

    February 6th, 2012 at 2:09 PM

    think it would help to show this to college students? nah, they will never believe it

  • Jim


    February 7th, 2012 at 1:14 AM

    This is a terribly unscientific study. White matter and grey matter ratios are what matter in the human brain, not comparative sizes of white matter. Also, look how small the sample sizes are.

    Schizophrenia is a psychological illness with several factors and simply looking at white matter doesnt cut it. Its as silly as scanning a person’s brain and saying they’ve got psychosis because they have less white matter!

    The fact remains, nobody has ever died from cannabis – its non toxic. Its not just teenagers that consume it, people of all ages and walks of life. We need to stop the biased propoganda and do proper clinical trials. What are legislators afraid of? the truth?

  • Charlotte LeBlanc

    Charlotte LeBlanc

    February 7th, 2012 at 8:10 AM

    Thank you for conducting this study. I really hope that this information reaches high schools and universities.

    My son was diagnosed with paranoid schizophrenia and bipolar disorder in 1997 at the age of 23. Through many trials and errors he is now able to live a normal healthy life; married, working, enjoying his passion (music) and medication free. And yes Cannabis was the trigger to his illness. Why do we know this? While smoking Cannabis he tried to stop his meds with the help of his psychiatrist. When he stopped smoking it, after 8 years, he was able to slowly (1 year and 4 months later) wean himself off his meds and live a normal life.

    I have written our family’s story and my son’s struggles and victories in conquering this dreadful illness. My hope is to spread the word to families and professionals who are faced with this epidemic of young adults with mental illness.

    My new book Sidetracked by Schizophrenia has been endorsed by Dr. Louis Thériault, Director of Psychiatry at Dr. George L. Dumont Hospital in Moncton, Dr. Peter Ford, Pharm D, Owner of Ford Apothecary, Eugene Niles, a mental health advocate and John Lutz, a registered social worker.

    My credentials are: my living experience with my son, a Bachelor of Applied Science in Nutrition, a Registered Holistic Allergist and certified Iridologist. Hope you enjoy it! Let me know if there is anything I can do to help.


  • Shaun


    February 7th, 2012 at 1:06 PM

    There are very few studies that follow the effects of cannabis.While it may reduce the white matter as has been noted by this study (with very few participants), in no way does it prove that cannabis usage leads to psychosis or anything like that.

    And if cannabis is indeed evil and bad and that is the reason it is illegal then cigarettes should not only be made illegal but an extraordinary punishment needs to be given out to cigarette manufacturers,not government help.

  • AliciA


    February 7th, 2012 at 5:38 PM

    It kills brain cells. Proof definitive right here.

  • bryan g

    bryan g

    February 8th, 2012 at 12:41 PM

    @AliciA:Thank you so much for your very informative comment *insert sarcasm here*

    Now you can go back and have your ‘relaxing’ drink while you fill your lungs with cigarettes made of tobacco grown with radioactive pesticides :D

  • Louis


    March 3rd, 2012 at 7:01 AM

    @Bryan g:

    What is it in Ms. Alicia’s comment that lead you to believe that she smokes and drinks? Could unfounded assertion be a manifestation of the reduced capacity for reason brought about by cannabis?

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