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New British Study Suggests Use of Potent Cannabis Increases Risk Of Psychosis

  1. Beenthere2Hippie
    A British study suggests the risk of psychosis is five times higher for regular users of cannabis, adding to a growing body of evidence linking drug use and mental health disorders. he six-year study published in the medical journal The Lancet on Monday (local time) reported on 780 people living in south London, 410 of whom were being treated for conditions including schizophrenia and bipolar disorder.

    The report's lead author was Marta Di Forti from the Institute of Psychiatry, Psychology and Neuroscience at King's College London, who warned about the growing use of "skunk" - a powerful type of cannabis. Compared with those who had never tried cannabis, users of high potency skunk-like cannabis had a threefold increase in risk of psychosis," she said. "The risk to those who use every day was even higher - a fivefold increase compared to people who never use," she added in a statement.

    Psychosis is a mental health problem and the symptoms include hallucinations and delusions. In England, about one new case of psychosis is diagnosed for every 2000 people every year.

    "This paper suggests that we could prevent almost one quarter of cases of psychosis if no-one smoked high potency cannabis," said Robin Murray, professor of psychiatric research at King's College London and a senior researcher for the study. This could save young patients a lot of suffering and the NHS (National Health Service) a lot of money," he said.

    The study (http://www.thelancet.com/pb/assets/raw/Lancet/pdfs/14TLP0454_Di Forti.pdf) was based on 410 patients who reported psychosis between 2005 and 2011. A further 370 healthy participants from the same area of south London were included for comparison. In 2010, a survey of 3800 young adults in Australia found an increased risk of psychosis for those who started smoking cannabis at an early age and used it for several years.

    Channel 3 News/Feb. 16, 2015
    Chart: The Lancet - Feb. 2015
    Newshawk Crew

    Author Bio

    BT2H is a retired news editor and writer from the NYC area who, for health reasons, retired to a southern US state early, and where BT2H continues to write and to post drug-related news to DF.


  1. Alfa
    This study is quite botched. I find it hard to believe that a reputable journal like the lancet has published it.

    They took two groups: psychotic and non-psychotic.
    Naturally the psychotic group smoked cannabis every days and more potent cannabis. I am not sure how they come to the conclusion that this means that potent cannabis causes psychosis. The first group naturally has a need to self medicate. The non-psychotic group does not. The study acknowledges that the psychotic group has this need, but then ignores it because they claim that self medication would lead to the use of varieties of cannabis with high cannabidiol.

    The study shows that the psychotic group uses tobacco more than the non-pyschotic group, but it does not draw the same conclusion as with high potency cannabis that there is a higher risk of psychosis. This is inconsistent.

    The next issue is that the people could choose between:

    1. Never used
    2. hash-like
    3. Skunk-like
    Hashish is supposed to stand for weak cannabis. Granted hashish in the UK is overall some weaker than hashish in European mainland. But hashish is merely the form and can be quite potent. The Dutch government measured up to 45% THC in hash. That's almost double the THC level of high potency cannabis bud.

    Skunk is supposed to stand for highly potent cannabis.

    This differentiation is so confusing and untrue that it does not seem like any reliable conclusions can be made from this study. I cant imagine that participants to the study could make sense of the questions about skunk and hash.
  2. Beenthere2Hippie
    I agree it is a confusing study and that clumping together psychiatric and non-psychiatric patients makes little sense, but The Lancet has published it so members of DF should probably be aware of the study's existence, if for no other reason than to debate its credibility.
  3. Alfa
    Yeah, it wasn't a criticism of the post.
  4. Beenthere2Hippie
    Thanks, Alfa. I will honestly sleep better knowing so. ;)
  5. MikePatton
    Regardless of this study - isn't their already a consensus regarding the effects of the THC/CBD ratio on psychosis? That is - THC can trigger a psychotic episode, but CBD is a strong antipsychotic, and therefore its presence reduces the risks associated with THC in that area.

    There was an expirement that I really like, where people were injected with either pure THC or a THC/CBD mixture. The results were very significant in confirming this hypothesis.
  6. Isodimorphism
    They could put a different spin on this story: hash reduces the risk of schizophrenia!

    But somehow, I can't see the press going for that...
  7. MikePatton
    Regarding the hypothesis I mentioned earlier, about the impact of the THC/CBD ratio on psychosis - this abstract lists some of the recent findings that support it. Again, to the best of my knowledge - this is the current consensus. Some disagree about whether CBD is an effective antipsychotic compared to conventional medication, but the hypothesis regarding the relationship between THC and CBD and its effect on psychosis is pretty scientifically sound:
    Zuardi et al., 2012,
  8. Alfa
    It seems that the assumption of the researchers is that the users of cannabis know what the CBD levels are in their cannabis. Another false assumption seems to be that a low potency strain equals high CBD levels.
  9. 5-HT2A
    To reiterate the above, the fact that CBD has been bread out of most cannabis, especially the skunk cannabis in question, seems to be of overriding importance. We shouldn't be condemning cannabis unnecessarily when we have the ability to breed strains with enough CBD to mitigate these problems.
  10. MikePatton
    Yes, that was exactly my point. The same way we inspect alcohol for Ethanol / Methanol ratio - we can inspect weed for THC / CBD ratio. But of course, in order to do that we'd have to regulate it... And therefore, legalize it.
  11. Isodimorphism
    I'd very much like to see a study on schizophrenic symptoms in users of sativa compared to users of indica. If a higher ratio of THC:CBD causes schizophrenic symptoms and a lower ratio reduces them, we'd expect to see fewer problems amongst indica users.

    Of course, this carries the same risk of self-medication bias as the main study: people with a tendency towards psychosis might be more likely to use indica because it treats their symptoms or at least doesn't aggravate them.
  12. MikePatton
    ^ Have you seen the one with the THC\CBD VS THC injections? That's pretty much what they tried to do there - they used an experimental design (as opposed to a correlational design, as in the study in the OP) which allowed them to infere casuallity, exactly what you're talking about. There's a filmed experiment of this on youtube, some british news reporter volunteered to be a subject.
  13. Scloud90
    I don't see how this would be surprising regardless of if the study is conclusive or inconclusive using the correlation causation fallacy.

    Any type of drug that is psychedelic or mind altering in any way could be linked with Schizophrenia.
    a drug doesn't have to literally create a mechanism that slowly drives you to being schizophrenic.

    All you need is a person with a genetic predisposition to a disorder that is expressed given a certain stimuli usually extended exposure to it.

    Schizophrenia isn't completely caused by external factors or genetics its a combination, the ratios being different in any case. Greater predispositions are shown with a strong family history of it, but doesn't necessarily make them a schizo given the circumstances of their enviroment and etc

    If cannabis caused schizophrenia by itself that wouldn't make sense. It can cause panic attacks or other things with certain type of people. It can also increase paranoia. A repetition of use despite a user experiencing these effects will more than likely cause a person with a predisposition to be a schizo to become one.

    We're not 100% certain on the exact causes like any mental disorder that causes schizophrenia. However given an understanding of how it can be caused could make this study not necessarily just a correlation that was a waste of everyones time, but could lead to future studies.

    We can find out if the correlation between it and cannabis is nothing more than a fallacy or if it's a puzzle piece to other links, such as if the amount of schizos decrease or increase with cannabis use if we narrow it down to those with greater predispositions to schizophrenia.

    We Can find out if the paranoia or panic that some may have experienced were an important factor in influencing their disorder or if it was just the actual plant itself per se....meaning is the weed the problem by itself or just the side effects.... it could be the case that those who experience certain side effects are more likely to develop schizophrenia on some level depending on their genetic background. Some people may get no paranoia at all from weed.

    All I'm saying is understanding how schizophrenia is developed may shed light on some things, and the more we find out is a win for preventing it and treating it. First we must find a lead(this correlation) before we can search for the smoking gun. I'll have to read this more later when I get some time i just saw some talk on the thread and thought I might put my 2 cents in it.

    I think we should focus on the disorders and not immediately worrying if weed is under attack. If we find a cause then we can genetically modify strains that are free from the risks of causing these disorders. That would be interesting to see happen, but if this link is a dead end might be a waste of time.

    If a strain is continued to be marketed under a lie or misinformation such as... this particular strain is schizophrenia free!!!! Then someone else is gonna get rich and it might end up all the other strains don't even get bothered with, and now everyone's pulling out a company branded marijuana joint, and before you know it everyone's bored of smoking the same shit.

    Imagine if medical research legalized cannabis in some areas but then tried taking over what strains were grown and regulated! That would suck for people who enjoy the variety of this plant. I however would only care in the sense that others are happy and reduce the lies that might be used to make money for corporations. I dont have any interest in smoking the stuff.
  14. xiaobendan
    The annoying thing is that this study will be quoted by people as gosple truth.

    I personally don't use it for many reasons: legal,social,psychological etc.

    But I feel this study will annoyingly be on the lips of former stoners who are so much better than their old comrades.

    Smoking excessive weed is mentally bad for you but not nearly as mentally and emotionally bad for you as daily morning to night drinking.

    Lets be honest weed only starts to really cause problem when you are waking up and having a bong before breakfast and rehitting every hour or two.

    If used once or twice a week it is a very good buzz.

    But I quit when I was 25 because I couldnt do that,and ten years a vegetanble was too long already.

    In general most people,like most drinkers, can use this substance with few problemsI
  15. Rob Cypher
    Scientists find link between skunk weed and psychosis; but that’s not the whole story

    Scientists have found a link between regular use of powerful so-called “skunk” marijuana and psychosis in some users. However, extracts of cannabis are being used to ease the symptoms of mental illness in other patients.

    New Scientist reported on a study by researchers at King’s College London who found that regular users of the powerful “skunk” were three times more likely to suffer from psychosis and that daily users were five times more likely.

    However, people who smoked regular hashish — which contains the same psychoactive ingredient as ultra-powerful marijuana strains, but is not as potent — showed no variations away from or toward psychosis.

    Team co-leader Robin Murray spoke to New Scientist about the study’s findings, which explored possible contributing factors in 410 people newly diagnosed with psychosis and compared their lives with a control group of 370 regular people with no history of psychosis.

    Psychosis is a blanket term for any mental state involving a disconnection from reality. Psychosis could mean any symptoms from mild to severe depression, temporary or lasting paranoia, slowed or impaired cognition, or other sensory disruptions.

    So-called “skunk” weed is the result of years of cultivation by marijuana growers interested in producing a more potent high in users. The new strains of pot are Murray said, “far richer than hash in delta-9-tetrahydrocannabinol, or THC, the ingredient that creates the drug’s high but which also triggers psychosis. Even more important, skunk contains hardly any of a substance called cannabidiol, or CBD, which has been shown to counteract the psychotic effects of THC.”

    Amir Englund, also of King’s College, said, “In traditional hash, the proportions of THC and CBD are about equal, at 4 per cent each. In skunk, THC reaches around 14 to 15 per cent, while CBC tumbles to barely a trace.”

    Englund reported that a U.K. company called GW Pharmaceuticals is reportedly having success using CBD to treat symptoms of psychosis in patients with schizophrenia.

    The company is testing 80 individuals in the U.K., Poland and Romania to see if doses of CBD calm their psychotic symptoms.

    Murray cited a German study that followed 33 patients with schizophrenia and found that CBD treated their symptoms as well as their prescribed medication, amisulpride, but without the prescription drug’s side-effects.

    David Ferguson
    Raw Story
    February 18, 2015

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