A lot of people believe that Cannabis causes schizophrenia
The link between smoking cannabis and developing schizophrenia is strong but in which direction does the causality flow. Does smoking cannabis cause schizophrenia or does having schizophrenia make you more likely to smoke cannabis? Research studies suggest that the second explanation is more likely.
A group at the Institute of Psychiatry, King’s College London decided to address this issue and reported their findings in the Molecular Psychiatry. They mined the genomes of over 2000 people and correlated the schizophrenia-related alleles with cannabis use (An allele is an “alternative” or different form of a gene). They identified a significant association between smoking cannabis and schizophrenia alleles. (Yes its a GWAS study!).
In a previous article, I discussed the nature versus nurture debate. Here we have a similar challenge: is the significant association between cannabis use and schizophrenia a result of shared genetic history or an incidental link which arose as schizophrenia sufferers resorted to self-medication. One of the most powerful tools to determine how much the environment or genetic factors contribute to a particular disorder is twin studies.
For this reason, this team of researchers analysed 990 twins and found that when both twins smoked cannabis they shared a greater portion of the schizophrenia risky alleles than when only one twin smoked or neither were cannabis users (See their results below).
These results suggest that yes there is a causation link between smoking cannabis and schizophrenia but it is in the opposite direction to the popular perception that cannabis smoking leads to schizophrenia. In other words, schizophrenia smokers are more likely to smoke cannabis rather than cannabis causing schizophrenia.
Why would schizophrenia sufferers resort to smoking cannabis? Perhaps as a form of escapism: A coping mechanism to overcome their symptoms and the everyday social stigma of this mental disorder. Perhaps something else? Who knows? After all, we are not simple dishes you can rustle up in the kitchen if you follow the instructions. (We have the recipe, it’s your DNA, but remember the environment plays a role too, and so do we ourselves!).
NB: This study does not definitively rule out that cannabis is not a risk factor for developing schizophrenia as even the authors point out that the causation could be bidirectional, meaning cannabis could make people more susceptible to developing schizophrenia and in turn once you have schizophrenia you resort to smoking cannabis.