Cannabis-Related Psychosis May Not Increase Risk for Schizophrenia

The subject of cannabis use and schizophrenia has been explored in depth in the past several years. There has been evidence of a clear link between cannabis use and psychotic episodes and a link between episodes of psychosis and the later onset of schizophrenia. But until now, no one has looked at how cannabis-related psychosis increases the risk for the development of schizophrenia. In addition, little research has looked at how this risk varies over time. To address these voids in research, Edison Manrique-Garcia of the Department of Public Health Sciences, Division of Social Medicine at the Karolnska Institutet in Sweden recently led a study that analyzed data from more than 50,000 individuals who had reported their experience with cannabis use throughout adolescence. The individuals remained part of a cohort that was evaluated over a 35-year period. It was from these data that Manrique-Garcia looked at the specific relationships between cannabis use, psychosis, and eventual schizophrenia.

The study revealed that the individuals who used cannabis regularly were almost four times more likely to develop schizophrenia than those who never used cannabis and more than twice as likely to experience a brief psychosis episode. The results also showed that the risk for future psychosis and schizophrenia weakened over the long-term. Manrique-Garcia said, “Of the cases related to cannabis use, 60% occurred during the first decade compared with 45% among non-users of cannabis.” However, the findings also demonstrated a clear relationship between dose and risk. In particular, those who used the highest amounts of cannabis for the longest periods of time had the highest risk of schizophrenia. This risk was increased by early episodes of psychosis, regardless of whether they were cannabis induced or not. The individuals who experienced episodes of cannabis-induced psychosis and those who had non-cannabis-related psychotic episodes were equally at risk for schizophrenia. But Manrique-Garcia points out that the individuals with cannabis-related psychosis may not have experienced any psychotic episodes if they had not used cannabis. Further research is needed to determine if this would ultimately decrease their risk for the later development of schizophrenia.

Manrique-Garcia, E., Zammit, S., Dalman, C., Hemmingsson, T., Andreasson, S. (2012). Cannabis, schizophrenia and other non-affective psychoses: 35 years of follow-up of a population-based cohort. Psychological Medicine, 42.6, 1321-1328.

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  • Gloria Childs

    May 18th, 2012 at 4:19 PM

    I would be very interested in knowing if the research that points to these types of correlations has ever been effectively used in just say no campaigns and other strategies to help curb drug use and abuse in teens. I know for a fact that if someone had ever told me this when I was experimenting with pot and other drugs it sure would have made me take a second look at the choices that I was making. Maybe I would have done the same things and then again maybe I wouldn’t have, but I sure would love to see how teenagers today would react to this.

  • cal

    May 19th, 2012 at 7:25 AM

    Look, pot screws with the brain.
    It does not matter if you smoke once a day or once a year, anything that makes you that fuzzy and impaired is doing some damage somewhere along the line.
    Doesn’t mean that you will see it in a week or even a year, but generally it’s going to come back tp haunt you eventually.

  • Lottie

    May 19th, 2012 at 12:27 PM

    I am not a strong advocate for marijuana, but I am not necessarily as much against it as some will be.

    What I would like to know however is how is there any clear proof that it is the use of marijuana that causes the development of schizophrenia in some people?

    In other words how do we know that they would not have debeloped schizophrenia anyway, whether they ever smoked marijuana or not?

  • Don Berry

    May 19th, 2012 at 2:17 PM

    “In particular, those who used the highest amounts of cannabis for the longest periods of time had the highest risk of schizophrenia.”

    Or, those who had the highest risk for schizophrenia were more attracted to cannabis for self-medication. The study then shows that, over time, the risk of schizophrenia declined.

  • tonydfixer

    May 20th, 2012 at 5:15 AM

    Young people should not take any drug that alters state of mind. I had not taken any cannabis until the age of 18, I had no psychosis or schizophrenia. I think when the brain is still forming it may be effected if subjected to some substances.

  • Hale

    May 20th, 2012 at 5:43 AM

    In so many of these studies that I see published on here many of them leaave you to wonder which ailment causes which. Sure there is evidence that smoking pot could cause greater likelihood of schizophrenia. But on the other hand you could reason it out like Done and say that maybe these patients were self medicating and were more attracted to using than someone else could have been. I know that with every study you have to begin with a hypothesis and if your study in any way shows that this was correct than that could lead to some real scientific breakthroughs. But I think that we still need to be careful and not jump to conclusions before jumping in head first into a conclusion that may or may not be all that it seems.

  • Anne

    May 20th, 2012 at 9:09 PM

    @Don Berry:Couldn’t have said it any better!

    @tonydfixer:I agree with what you say. I started marijuana when I was 19 and now 3 years later I have only good things to say about it. Adolescents should not be allowed to use it. Responsible adult usage is the way to go!

  • j

    May 21st, 2012 at 2:19 AM

    This is a fine example of correlation trying to pass itself as cause and effect…when it’s just correlation. Before any clinical treatment, a very high percentage of those with mental illnesses; try to self medicate using a variety of substances, as another poster pointed out.

    If someone is experiencing anxiety, depression, sleeplessness, they will turn to anything that alleviates those symptoms. Of course this seems to confound the medical community…who seems to think if someone is having such problems, then they would seek out medical help. Which is certainly not the case…if people did not want to self medicate then, there wouldn’t be such a large vitamin and supplement market, homeopathic medicines etc.

    A lot of people are afraid of doctors, don’t want medical bills, don’t have insurance, and a whole host of other reasons to self medicate. In the place of schizophrenia, put the term cancer, HIV, or anything else and you will find the same correlation, that is not a cause nor effect of alternative medicines.

    Also, think if the social stigma of using some alternative medicines, the only reason cannabis causes what seems like a paranoid psychosis is because of the illegality of the drug. Just read the history of how paranoid people were of getting caught, arrested, or persecuted during alcohol prohibition…and you will see a similar psychosis that is directly related to it’s illegality.

  • erin

    May 22nd, 2012 at 4:40 PM

    I completely agree with J. These are not going to be the folks who are turning to a medical doctor for help especially when it comes to something like this. They are likely trying to help alleviate many of the symptoms that they are experiencing. And yeah, would be such a big deal if it was a cancer patient seeking treatment in this way? No because that would be considered acceptable.

  • Charlotte LeBlanc

    May 22nd, 2012 at 5:18 PM

    Thank you for conducting such studies. My son lived with cannabis induced schizophrenia for eight years. When he stopped consuming cannabis, he was able to wean himself off his medication and is now leading a normal life medication free.
    Keep up the good work in educating people in mental health awareness!

  • focusonpeace

    May 24th, 2012 at 9:15 AM


    So glad your not head of the scientific research. There are people who smoked cannabis all their life and have had NO negative out come only positive. It varies from person to person. Also some one could develop psychotic symptoms regardless, but happen to be smoking cannabis…do you find the cause? Or blame cannabis. I know which is easier…

    Funny how they didnt mention the CBD in cannabis has anti-psychotic properties.

  • NoName

    May 28th, 2013 at 6:06 PM

    First of all, usually marijuana these days contains 10-15% THC and 0.1-0.5% CBD, which makes the CBD claim worthless.

    Another finding, the “self-medication” claim has been disproven at least once:

    I won’t go into much details, but I know people who have become schizophrenic from marijuana with no family predisposition whatsoever. Who are you to deny that, or to deny the work of those doctors who make these studies with no medical knowledge.

    The most important thing is that, effectively, there has been NO EVIDENCE WHATSOEVER that “marijuana is smoked to self-medicate psychotic symptoms”, and what HAS been proven is that marijuana usually makes symptoms worse. Only CBD alone could possibly have some benefits, and it triggers no euphoria.

    So all of you stoners, don’t escape the facts and the claims. At least, you are now more informed about your habit, more than those pro-marijuana activists that have no other motivation than political or monetary gain from it, or recreational uses intended – which is connected.

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