Marijuana Use Can Cause Schizophrenia

This statement can be made based on the Bradford Hill criteria. Visit the IASIC library to read more about the Bradford Hill criteria and various adverse effects of marijuana.

People argue the difference between causation and association. This was the same argument held 100 years ago with tobacco. How can one prove that black lungs and cancer were caused by tobacco?  It could have simply been an environmental association. The proof that tobacco caused cancer and lung disease, and not just associated with these diseases was made using the epidemiological criteria established by Sir Austin Bradford Hill in 1965.

What is psychosis?  Psychosis is a symptom of disruption to a person’s thoughts and perceptions that make it hard for them to differentiate what is real what isn’t. It includes hallucinations, seeing, hearing or feeling things that are not there. It also includes delusions, strong beliefs that are not true and seem irrational to others such as external forces controlling thoughts or believing in special powers. Psychosis is a symptom of schizophrenia.

What is schizophrenia?  Schizophrenia is a serious mental illness that distorts thinking, emotions, making decisions, and relating to others.

What is the difference between cannabis and marijuana?  According to the NIH, National Institute of Health, cannabis refers to all 540 chemical substances in the Cannabis sativa plant.  The term marijuana refers to parts or products of the Cannabis sativa plant that contains substantial amounts of THC, the psychoactive chemical. The medical literature uses the term cannabis and marijuana, and therefore IASIC uses both terms.

How can we prove that cannabis/ marijuana causes chronic psychosis or schizophrenia? The proof comes using various medical research articles that fit the 9 Bradford Hill criteria.

  1. Strength of the association
  2. Consistency and reproducibility of the evidence
  3. Specificity
  4. Temporality, the effect occurs after the cause the effect
  5. Biological gradient, a dose-response relationship
  6. Plausibility
  7. Coherence
  8. Experimental evidence
  9. Analogy – other drugs of abuse increase dopamine release in the brain and can result in a chronic psychotic disorder.

The currently available research on cannabis causing chronic psychotic disorders satisfies the Bradford Hill elements of causation. This means that some people who develop a chronic psychotic disorder after using cannabis, would not have developed the disorder had they not used cannabis. Even if there is some confounding effects, for example unquantified variations in other environmental risks or in genetic background, it is not enough to undermine the effect of cannabis as an independent risk factor for psychosis.

Visit the IASIC Library, filed under Psychosis, to find the article titled: The Bradford Hill Analysis of Causation Applied to Cannabis Use and the Development of Chronic Psychotic Disorders by Christine L. Miller, Ph.D., Catherine Antley, MD and Dean Whitlock (editor) with a review and contributions from Carsten Hjorthoj, Ph.D., Associate Professor, Copenhagen Research Center for Mental Health, University of Copenhagen.

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