Effects of Marijuana May Increase Risk of Schizophrenia in Young Males

While the effects of marijuana on the developing brain has been a serious subject of debate, one recent study has conclusively found a link between marijuana use and schizophrenia. With the mass spread of medical and recreational marijuana legalization, it’s important for people to realize that it is not a benign drug (no drug is) and that there can be consequences for use.

Last August, the study was published in the Journal of the American Medical Association. It suggested that using marijuana during the teen years may increase the risk of developing schizophrenia – namely, if they genetically disposed to the illness.

Dr. Tomas Paus, Rotman Research Institute:

“If there is a family history of severe psychotic disorders, I would really encourage kids to avoid cannabis altogether. If you know these disorders run in your family, then I would be super, super careful.”

The study included nearly 1600 participants from age 12-21. Researchers obtained brain scans and data from 3 separate large studies.

The results were troubling – men who reported marijuana use in their early teens had a noticeably thinner cerebral cortex than others. However, that was only if they had a high genetic risk for schizophrenia. Also, low-risk men and women did not seem to be affected in the same way by marijuana use. This may be partially due to the fact that schizophrenia tends to develop earlier in men than women.


“There is a lot of restructuring going on in the male brain between the age of 12 and 18.”

“It seems that whatever it is in men, it basically makes them more susceptible to it,”

The cerebral cortex contains many receptors that bind to marijuana’s main psychoactive ingredient, THC. Additionally, testosterone contributes to changes in the cerebral cortex, and may, in some manner, interact with this substance.

Dr. David Goldman, Laboratory of Neurogenetics at the U.S. National Institute of Alcohol Abuse and Alcoholism reiterates that cannabis is not harmless:

“The burden of cannabis’ effects may fall more heavily on people who, because of genetic makeup or early life exposures, are at greatest risk for brain structural changes, psychosis or addiction. It is safer not to expose people to psychoactive drugs.”

What is Schizophrenia?

Schizophrenia is a chronic and often severe mental illness that affects thinking, feelings, and behaviors. Sufferers often feel as if they are disassociated from reality. Symptoms usually begin between the ages of 16-30, but can occur outside of this window.

Scientists believe that many genes can increase the risk of schizophrenia, but no single gene is responsible for the disorder. Genetic information can not yet be used to predict who may develop the condition. There may also be environmental factors which contribute to its development, including fetal malnutrition and virus exposure.

Signs and Symptoms

  • Hallucinations and delusions
  • Disorganized thinking
  • Agitated body movements
  • Reduced expressions of emotion and pleasure
  • Difficulty beginning and maintaining activities
  • Reduced verbal capabilities
  • Difficulty understanding information and making decision
  • Difficulty focusing and reduced attention span
  • Memory problems such as inability to process information immediately


It’s important to understand that every psychoactive substance has risks, it’s just a matter to what extent. I don’t believe that any sane person believes that marijuana is as harmful as say, alcohol or heroin, but no substance is “safe”. Effects of marijuana are not always predictable.

With the growing acceptance of marijuana, this is an important finding. Especially considering males, statistically speaking, are more likely to use marijuana, and the teenage years are a very common period of experimentation. Furthermore, there is no way to no for sure if someone is predisposed to schizophrenia.

~ G. Nathalee Serrels, M.A., Psychology