Cannabis and Psychosis; Is there a link?

The legalization of marijuana has been a widely debated topic over the past few years, especially after Colorado’s legalization was so beneficial to their public system. The proceeds are helping with school programs and lowering the incarceration amounts, among other things. Marijuana is touted by many people as a wonder drug that can assist in curing all kinds of illnesses, such as the nine year old autistic boy given cannabis oil speaking letters and words for the first time. It has to be said that this oil is non-psychoactive, so it is not the same as recreational marijuana. One study lists multiple ailments that can be treated with cannabis, including anorexia, multiple sclerosis, Parkinson’s, and others (Kogan & Mechoulam,2007).  That is to say, there are many available benefits that can be obtained through cannabis use,  but what are the risks?

Something that I have been wondering about for a few years, especially as more people close to my age started smoking marijuana, is if it affects those with mental illness negatively.

In Scott McGreal’s article, he states that there is a possibility that cannabis could be a direct cause of psychosis, but it is also possible that a confounding variable is causing the results studies are obtaining. It dealt with a specific type of psychosis that people with schizophrenia typically experience.

The issue with a lot of the studies is that they did not check for genetic factors, or other drug use such as amphetamines. So it is hard to get direct, proper results when you are unable to get a clear test and control group.

He also states that a more recent study has argued that the genetic risk of schizophrenia is what will also often influence people to use cannabis; the basic argument of this one study was that genetic risk will contribute to schizophrenia more than cannabis use: if it does, at all (McGreal, 2014).

Another study mentioned is one that defines schizotypy as  “experiencing unusual perceptions (e.g. feeling that strangers can read you mind) and holding peculiar beliefs about the nature of reality (e.g. that aliens are influencing events on earth)” (McGreal, 2014).  According to a review of multiple research studies, heavy users of cannabis are generally very high in this compared to those who do not use. Once again, this is a question of correlation as we cannot directly manipulate if someone is predisposed to schizotypy traits before we make them test marijuana.

A large issue that comes with attempting to research this type of data is ethics. It would not be ethical, if we assume that marijuana use contributes to the appearance of a mental illness in certain people, to force it upon them and use them as a test group. If it’s possible that without this exposure they may never develop traits of schizotypy or psychosis with schizophrenia, so our research is very limited. Case study data is more available in places where marijuana is legalized, however there are not that many places and those figures are still inconclusive as to whether or not one causes the other.

All in all, the only conclusive statement that can be made about cannabis and psychosis is that it MIGHT have an effect on the developing brain of an adolescent and cause an early onset of their schizotypy symptoms, or symptoms of schizophrenia.

Have you seen any studies that try to answer this question, that aren’t simply correlational?

Edited by Ranine Swaid.