Minimal Relationship Between Cannabis And Schizophrenia Or Psychosis, Says Study

By chillinwill · Oct 24, 2009 · ·
  1. chillinwill
    Last year the UK government reclassified cannabis from a class C to a class B drug, partly out of concerns that cannabis, especially the more potent varieties, may increase the risk of schizophrenia in young people. But the evidence for the relationship between cannabis and schizophrenia or psychosis remains controversial. A new study has determined that it may be necessary to stop thousands of cannabis users in order to prevent a single case of schizophrenia.

    Scientists from Bristol, Cambridge and the London School of Hygiene and Tropical Medicine took the latest information on numbers of cannabis users, the risk of developing schizophrenia, and the risk that cannabis use causes schizophrenia to estimate how many cannabis users may need to be stopped to prevent one case of schizophrenia. The study found it would be necessary to stop 2800 heavy cannabis users in young men and over 5000 heavy cannabis users in young women to prevent a single case of schizophrenia. Among light cannabis users, those numbers rise to over 10,000 young men and nearly 30,000 young women to prevent one case of schizophrenia.

    That's just part of the story. Interventions to prevent cannabis use typically do not succeed for every person who is treated. Depending on how effective an intervention is at preventing cannabis use, it would be necessary to treat even higher numbers of users to achieve the thousands of successful results necessary to prevent a very few cases of schizophrenia.

    Matt Hickman, one of the authors of the report recently published in the journal Addiction, said that "preventing cannabis use is important for many reasons -- including reducing tobacco and drug dependence and improving school performance. But our evidence suggests that focusing on schizophrenia may have been misguided. Our research cannot resolve the question whether cannabis causes schizophrenia, but does show that many people need to give up cannabis in order to have an impact on the number of people with schizophrenia. The likely impact of re-classifying cannabis in the UK on schizophrenia or psychosis incidence is very uncertain."

    Journal reference:

    1. Hickman et al. If cannabis caused schizophrenia-how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations. Addiction, 2009; 104 (11): 1856 DOI: 10.1111/j.1360-0443.2009.02736.x

    Adapted from materials provided by Wiley-Blackwell, via EurekAlert!, a service of AAAS.

    October 22, 2009
    Science Daily

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  1. Nature Boy
    Good solid science debunks yet another one of Frank's over-exaggerated risks. In a sense, cannabis has become the new ecstasy over the past few years. Fear campaigns being spread over the use of a drug that is generally safe if used correctly. Thanks for posting this up chillinwill. I'd rep you but I need to spread it around. It would great to see this study put right in the face of some politicians. It's about as conclusive as it gets in terms of uncovering their blatant lies.
  2. 420massacre
    thats pretty interesting post, could it always have a connection to bipolar?
  3. 420massacre
  4. chillinwill
    The study can be found Here thanks to corvardus
  5. Phenoxide
    While I appreciate the message they are trying to convey, the tone seems to be surprisingly political for peer-reviewed publication. As a scientist I really dislike the 'how many people to avoid one case' structure. They also have been quite selective in what they present. It's great that they reiterate that the risk of schizophrenia directly attributable to drug use is very low to the general population. The government would like people to believe that the occasional cheeky smoke will send them to the mental ward, so it's good to put things into perspective, especially for light cannabis users.

    However they do not present figures from a similar analysis for 'high risk' individuals (e.g. those with mental illnesses in the family, history of depression etc.). I suspect that for this subset of the population, drug use is a far more significant contributing factor to precipitation of schizophrenia. They also do not present a similar analysis for mental illnesses other than schizophrenia. My gut (i.e. unsubstantiated) feeling is that there is a stronger correlation between heavy cannabis use and mental illness in general than there is with the significantly genetic schizophrenia spectrum. Interesting article, but I wouldn't take it as conclusive proof that heavy cannabis use is necessarily safe.
  6. corvardus
    My pet rabbit's pet python who is also a scientist raised an eyebrow at the tone and language of the publication. Whilst I can't speak for the authors of the article the language is that which the government will like and if noticed will probably give it some credibility.

    Indeed with the line "The key strength of our study is that our estimates
    are transparent, but they also serve to illustrate several important factors and limitations that need to be considered by policy-makers.
    " that this article is intended for the eyes of government officials.

    When the government actually chews the numbers they will quickly find that the financial resources necessary to save just one individual from shizophrenia is going to be prohibitive, most likely more than just treating the condition in the first place.

    It is a round about way of going about it, but to my rabbit's pet python it makes some sense to adopt the tone and style they have in order to resonate with the policy makers.

    Most scientists would look past the tone to the statistics.

    I do not see why. These types of analysis if I am not mistaken is used in political circles as a cost/risk/benefit analysis when allocating financial resources. With each individual having an associated cost.

    It would make sense for a scientist to use the parlance of the politician when they are trying to communicate with them! :)

    Whilst I am not disagreeing with you the analysis is for a "generic" population. The factors that exaccerbate the problem still need to be ironed out in peer-review so whilst I dislike the conclusions they have made there is still merit in them.

    Given the following exerpt:
    In contrast, the NNT has been estimated as: 108 for appropriate statin treatment to prevent heart disease deaths [19]; 1224 for breast cancer screening to prevent one death after 14 years [20]; and 8.5 for web-based self-help to reduce drinking among problem drinkers [21].
    I think with certain rose coloured glasses taken off the financial investment necessary for the government to implement blanket investment to prevent cannabis exacerbated shizophrenia is essentially a non-starter even with choosing the lowest of numbers given the comparisons above.
  7. whitenoise
    I highly doubt that Bi-Polar disorder has any relation to marijuana consumption. Bi-Polar is viewed by most people to be a hereditary illness. Marijuana could trigger episodes of mania or depression in a patient with Bi-Polar but not the actual illness.
  8. 420massacre
    ya, swim seems to get that that when he blazes, he is more angry when he is on drugs then when he is off them. he is still trying to diagnosed bipolar. its taking longer then he expected.
  9. Kittty
    Swim thinks that there is not a relationship between weed and mental disorders. But Swim does think that drugs might bring out a mental disorder early in a person. b.c like the great bob marley said When u smoke the herb it reaveals it self to you. I know that is not scientific evidence but this article is quite flawed in its reasoning. Swim does not think that if you smoke weed you have a higher chance of having a mental disorder. Swim thinks if you have a mental disorder then if you smoke weed, or do mushrooms, it will be revealed to you earlier in life.
  10. rawbeer
    I think Kitty gets it right - if you have mental issues, don't do drugs. It won't be good for you and it gives jerks an excuse to pin your disorder on the drug. This topic comes up again and again here and it's really frustrating that college educated people can't grasp the fact that in any given population, there's going to be a few crazies. Their logic can be used to tie anything to disorders, they're just choosing pot. I've seen a drunk schizophrenic, and I've seen the same guy high on weed, and I'll take him on weed any day of the week. Ironically the worst he ever was was drunk and on antidepressants. But none of these drugs were the cause of his problem.
    This has also come up before, but I'll say it again - how much time and money does the British government waste on their nonsensical efforts to revert cannabis perceptions back to the 1940's? They make right-wing americans look like buddies of Jack Herer in comparison. I guess they get bored cramped up on that little island...
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