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Study: High-potency cannabis may increase risk of psychosis

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LONDON — Regular marijuana users might want to think twice before lighting up another joint of “chronic” or “skunk” weed, a new study suggests.

According to a study of 780 people by King’s College London’s Psychiatry, Psychology and Neuroscience department, the risk of psychosis is five times higher for those who use high-potent cannabis every day compared to non-users.

The study, first analyzed by the BBC, claims that regular marijuana users who use a milder form of the drug with lower THC content are not associated with increased risk of psychosis, defined as delusions or hallucinations that can be present in certain psychiatric conditions. However, those who smoke high-potent cannabis were linked to 24 percent of new psychosis cases analyzed in the study.

Researchers fear that as high-potency cannabis becomes more easily found and use more widespread, we could see in increase in conditions such as schizophrenia and bipolar disorder.

“Compared with those who have never tried cannabis, users of high potency skunk-like cannabis had a threefold increase in risk of psychosis,” Dr. Marta Di Forti, the lead author on the research, told the BBC.

The research was carried out over several years, and compared 410 patients aged 18-65 who reported a first episode of psychosis with 370 healthy participants in the same age range.

“Indeed skunk uses appears to contribute to 24% of cases of first episode psychosis in south London,” the study’s authors said.

Researchers said the findings underscore the need for increasing drug education, and a sharp reminder that no drug use comes without risks.

“Our finding show the importance of raising awareness among young people of the risks associated with the use of high-potency cannabis,” the study’s authors wrote. “The need for such public educations is emphasized by the worldwide trend of liberalization of the legal constraints on cannabis and the fact that high potency varieties are becoming much more widely available.”

Recreational marijuana use is legal in Washington state.

To read an excerpt of the study, click here. For the BBC’s story on the study, click here.

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  • mike van voorst

    now lets see the results of drinking a pint of whisky and 10 pints a day and see what we get. and this study was conducted in the UK where drug possession is treated way differently than in the US no wonder people are paranoid.

    • Chris Yeager

      Alcohol is self regulating. The amounts you assert would kill most People. Pot mixes with Alcohol and infusion into alcohol is already a business. Unfortunately Pot is well tolerated by the human physiology… The brain is what is affected. I guess we need more psychos….

  • dg54321

    How many of those who “developed” psychosis already had it but were undiagnosed? It’s been known for some time that those already suffering from some form of psychosis can have that ailment aggravated by heavy marijuana use.

    In the end, the benefits and lack of harm caused by not placing otherwise innocent people in jail for using a plant they were going to use anyways far outweighs the harm caused by aggravating potential psychoses in certain users.

  • Jose Ruiz

    Your study is just junk, is not the type or strength of marijuana is the psychotic individual. You are trying to connect this two, those individuals psychos where psycho before using marijuana, up there go your study down in flames.

  • more lies...

    Cannabis does not in way shape or form cause psychosis. Although, it can bring psychosis forward early to someone that is born with psychosis. Psychosis can take 20 + years to show up regaurdless of cannabis use. Billions of people have used cannabis for thousands of years. If pot causes psychosis wouldnt there be some kind of proof or signs? I mean our parents/ grandparents / aunts/ uncles / cousins/ brothers / sisters have all most likely tried pot or lived through the 60’s. Do they have psychosis? Dont be fooled by this OLD b.s.

  • Paul Pot

    You guys have no idea how naive you look.
    Most people are experienced with cannabis these days and we’re all wondering what your talking about.
    Where can I get some of this amazing Skunk that will destroy my brain?
    I’ve been looking for it for 30 yrs and never got close to it.

  • stel1776

    If cannabis was a significant cause of psychosis, then varying rates of cannabis usage over time in the U.S. and other countries should have a corresponding change in rates of psychosis in those countries, but they have not despite decades of use by millions. Also there is no correlation of individual country cannabis usage rates with their rates of psychosis when comparing these rates for various countries throughout the world.

    “The most parsimonious explanation of the results reported here are that the schizophrenia/psychoses data presented here are valid and the causal models linking cannabis with schizophrenia/psychoses are not supported by this study.”
    Frisher et al. Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005. Schizophr Res. 2009.

    “There was a steep rise in the prevalence of cannabis use in Australia over the past 30 years and a corresponding decrease in the age of initiation of cannabis use. There was no evidence of a significant increase in the incidence of schizophrenia over the past 30 years”
    “Cannabis use does not appear to be causally related to the incidence of schizophrenia…”
    Degenhardt et al. Testing hypotheses about the relationship between cannabis use and psychosis. Drug Alcohol Depend. 2003.

    “The current data do not support low to moderate lifetime cannabis use to be a major contributor to psychosis or poor social and role functioning in high-risk youth”
    Auther et al. Prospective study of cannabis use in adolescents at clinical high risk for psychosis: impact on conversion to psychosis and functional outcome. Psychol Med. 2012.

    This recent study found that alcohol may contribute to psychosis, but not cannabis:

    “Results revealed that low use of alcohol, but neither cannabis use nor tobacco use at baseline, contributed to the prediction of psychosis in the CHR sample”
    Buchy et al. Impact of substance use on conversion to psychosis in youth at clinical high risk of psychosis. Schizophr Res. 2014.

    There are other explanations for an association between cannabis use and psychosis:

    “The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.”
    Proal et al. A controlled family study of cannabis users with and without psychosis. Schizophr Res. 2014.

    “these findings suggest that part of the association between schizophrenia and cannabis is due to a shared genetic aetiology”
    Power et al. Genetic predisposition to schizophrenia associated with increased use of cannabis. Molecular Psychiatry. 2014.

    One of the most important confounders is the fact that cannabis helps some people with schizophrenia, especially varieties high in cannabidiol (CBD), a cannabioid which can treat and prevent psychosis:

    “Additionally, CBD prevented human experimental psychosis and was effective in open case reports and clinical trials in patients with schizophrenia with a remarkable safety profile…These results support the idea that CBD may be a future therapeutic option in psychosis, in general and in schizophrenia, in particular.”
    Zuardi et al. A critical review of the antipsychotic effects of cannabidiol: 30 years of a translational investigation. Curr Pharm Des. 2012. Review.

    “…but cannabidiol displayed a markedly superior side-effect profile. Moreover, cannabidiol treatment was accompanied by a significant increase in serum anandamide levels, which was significantly associated with clinical improvement. The results suggest that inhibition of anandamide deactivation may contribute to the antipsychotic effects of cannabidiol potentially representing a completely new mechanism in the treatment of schizophrenia.”
    Leweke et al. Cannabidiol enhances anandamide signaling and alleviates psychotic symptoms of schizophrenia. Translational Psychiatry 2012.

    “Effect size differences in cognitive performance in the schizophrenia group as a function of cannabis use were in the small to medium range, denoting superior performance in cannabis-using patients.”
    Rabin RA. The effects of cannabis use on neurocognition in schizophrenia: a meta-analysis. Schizophr Res. 2011.

    Correlation does not imply causality. There are many factors involved, including the fact that many with undiagnosed schizophrenia are self-medicating with cannabis. It is especially difficult to tease out this confounder when trying to establish causation.

    On a related note, interestingly, patients with psychotic disorders who used cannabis had a lower mortality risk than those who did not:

    “ten-year mortality risk (5.5% vs. 13.6%) was lower in cannabis users than in non-users with psychotic disorders”
    “We observed a lower mortality risk in cannabis-using psychotic disorder patients compared to cannabis non-users despite subjects having similar symptoms and treatments”
    Koola et al. Alcohol and cannabis use and mortality in people with schizophrenia and related psychotic disorders. J Psychiatr Res. 2012.

  • John

    I know a lot of people in their mid-forties and older who have had to stop smoking marijuana because the new breeds are too potent and cause panic attacks,paranoia and hallucinations if too much is smoked,and when I say too much I mean 2-3 hits.
    The older strains like Columbian Gold,Panama Red,etc. you could do 4,5,6 hits and know where you were in the high.Today if you smoke 1/2 hit too much you could lose it!Also the old strains you’d top out a high,the new stuff you could put yourself into a dangerous mental state.

    Yeah they are legalizing the new stuff because it is dangerous – and who knows what they’re hybridizing it with! It will zonk you and put you in a brain dead state whereas the old stuff would make us laugh and put us in a transcendent state.Two different kinds of highs and a damn shame you can’t find the old safer strains anymore.

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