Marijuana and Schizophrenia - Examining Causation and Correlation

Science has uncovered a definite link between marijuana and schizophrenia, with a complicated array of biological mechanisms and markers involved. In my own anecdotal bank of knowledge, I have memories of psychology class, where my teacher warned us of the encounters she had with teenagers whose first try of the drug triggered an onset of schizophrenia. As we've learned in class, everything carries a risk. But I was very curious about whether or not all of us carried the same risk of schizophrenia, or if abstaining from marijuana was an encourageable strategy to delay the onset of the disease.

Very recently (Oct. 11th), a report came out about study mentioning the NRG1 gene, suggesting that the NRG1 gene is a susceptibility gene for marijuana dependence. The NRG1 gene originally came into the awareness of scientists when it was been found to be implicated in schizophrenia risk. While these findings indicate that schizophrenia and marijuana dependence could likely be caused by a common gene, the author of the article reiterates that "a number of epidemiologic studies have attributed the association... to the effects of cannabis on the brain rather than a common genetic link between these two conditions."

John Krystal, editor of Biological Psychiatry, comments on the study's findings in relation to our established knowledge: "the current data provide a potentially important insight into the heritable risk for schizophrenia and raise the possibility that there are some common genetic contributions to these two disorders." Thus, despite the hints at causation in these findings, scientists have accepted the correlation but not causation.

Looking further into it, I dug up some statistics that add questions to the nature of the correlation. An article in Time Magazine speaks of studies finding that people with schizophrenia are twice as likely to smoke marijuana as those without. At the same time, those who smoke marijuana are twice as likely to develop schizophrenia as nonsmokers.

So which came first? The chicken or the egg? Do schizophrenics gravitate towards marijuana use, or do marijuana users trigger brain changes leading to schizophrenia?

There's evidence for both in the psychological and biological research fields.

  •  Schizophrenics gravitate towards marijuana use: In the article in mentioned a psychological study conducted in Holland regarding mood and marijuana use habits, "all participants, not surprisingly, reported feeling happier when they were high, but the mood-lifting effect of marijuana was stronger among smokers with schizophrenia. Unlike people without the disease, schizophrenia patients also reported a reduction in negative feelings after smoking marijuana."
  • Marijuana use triggers brain changes that lead to schizophrenia: Along with the genetic research above, other studies link cannabis and schizophrenia with neural changes. In this experimental study, the gamma-aminobutyric acid (GABA) system, the endocannabinoid system and cannabis' affect on them is examined. The study found that irregularities in the GABA system, and subsequently in the endocannabinoid system are found in schizophrenia. These irregularities are a result of early (adolescent-age) exposure to cannabis. Again, John Krystal comments: "While the whole story is still developing, from these data, it looks like developmental deficits in GABA systems are sufficient to disturb the function of the endocannabinoid system. This could be an important clue to the link between cannabis use and psychosis."

Despite a huge array of research on the topic, some skeptics still maintain the possibility that the link between the two could be coincidental. At the moment, the amount of variables involved - genetics, brain structure, psychology, general behavior- seems overwhelming, and make identifying the specifics of this correlation extremely difficult. We also don't know the independent and dependent variable - schizophrenia could come first, or marijuana use. Possibly, these variables vary from case to case. Which makes it hard for me to conclude anything.

I wouldn't go to extremes and say that marijuana causes schizophrenia - it seems there are biological prerequisite that must exist in order for it to affect a person that way, so we all carry a different, unknown risk. At the same time, avoidance of marijuana seems reasonable if you're still young, since one of the above studies mentioned the particular vulnerability of adolescents to GABA and endocannabinoid system disregulation. After reading my blog, what will you guys do, and has your perception of the risk of marijuana use changed?

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