Marijuana Can Increase Risk Of Psychotic Illness Later In Life By Over 40%
    By News Staff | July 26th 2007 05:41 PM | 9 comments | Print | E-mail | Track Comments
    There is now enough evidence to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life by more than 40%, conclude authors of an Article published in this week’s edition of The Lancet. “Governments would do well to invest in sustained and effective education campaigns on the risks to health of taking cannabis.”

    Cannabis, or marijuana, is the most commonly used illegal substance in most countries, including the UK and USA. Up to 20% of young people now report use at least once per week or heavy use (use on more than 100 occasions).

    Dr Theresa Moore, University of Bristol, and Dr Stanley Zammit, Cardiff University, Wales, and colleagues did a meta-analysis of 35 studies, dated up to 2006, to assess whether there was evidence to connect cannabis use to occurrence of psychotic or mental health disorders.

    They found that individuals had used cannabis ever were 41% more likely than those who had never used the drug to have any psychosis. The risk increased relative to dose, with the most frequent cannabis users more than twice as likely to have a psychotic outcome. Depression, suicidal thoughts, and anxiety outcomes were examined separately, and findings for these outcomes were less consistent, with fewer attempts made to address non-causal explanations than for psychosis.

    The authors say that recent estimates of the proportion of young adults and adolescents who have ever used cannabis is 40%. If having ever used cannabis increases the risk of a psychotic outcome by 41%, about 14% of psychotic outcomes in young adults in the UK would not occur in cannabis were not consumed.

    The authors say: “We have described a consistent association between cannabis use and psychotic symptoms, including disabling psychotic disorders.”

    They conclude: “Despite the inevitable uncertainty, policymakers need to provide the public with advice about this widely used drug. We believe that there is now enough evidence to inform people that using cannabis could increase their risk of developing a psychotic illness later in life.”

    In the accompanying Comment, Drs Merete Nordentoft and Carsten Hjorthøj, Copenhagen University Hospital, Denmark say: “In the public debate, cannabis has been considered a more or less harmless drug compared with alcohol, central stimulants, and opioids. However, the potential long-term hazardous effects of cannabis with regard to psychosis seem to have been overlooked, and there is a need to warn the public of these dangers, as well as to establish a treatment to help young frequent cannabis users.”

    Source: Cannabis use and risk of psychosis in later life


    Were these studies case-controls or were they cross-sectional? It would be more interesting to know whether these currently mentally ill people were simply using the marijuana in order to alleviate their psychiatric prodromal symptoms in their youth, as opposed to having used the marijuana, and then it later having actualy caused their psychiatric illness. To think of how many people smoke marijuana in this country (even if they won't admit to it), it would be outrageous to consider that they all have a 40% chance of mental illness in the future. Is that much of our country really considered "mentally ill"?

    I don't know about this study in particular, but several other studies have found that psychosis disorders per se do not predict future cannabis use, but cannabis use does predict future psychosis disorders. Also, the risk for future psychosis disorders is generally related to quantity and frequency of use in a dose dependent fashion, suggesting causation. High potency use or daily or near daily use during adolescence are also linked to increased rates of psychosis disorders down the road.

    Gerhard Adam
    There's no "suggestion" of causation.  Until you can establish that such psychological disorders aren't precursors to psychosis and that they aren't the drivers to increased [or daily] cannibis use, then you have nothing except confirmation bias.

    That's no different than most of the arguments around "gateway" drugs, where they choose an obvious element and then attempt to extrapolate causation.  That would be like arguing that water is a gateway drug because all alcoholics started off drinking water as children.
    Mundus vult decipi
    Some of the longitudinal studies have, in fact, controlled for the likely precursors. You don't have to take my word for it, do some research yourself. The abstracts and articles are available on the Internet. You might start with the review of the literature by Moore et al. in The Lancet, I believe it was in the Fall of 2008, which caused The Lancet to reverse its previous editorial position that marijuana did not contribute to mental health problems.

    Gerhard Adam
    I also question these findings, since it would seem difficult if not impossible to differentiate those individuals that may well have been self-medicating with cannabis and therefore skew the statistics.  I'm also not clear on how they managed to separate out cannabis from all the other potential drugs that a patient may have been using over a lifetime.

    It would also seem that there should be some identifiable change in the brain biochemistry or some other brain pathology that would be useful in establishing a causal link.
    Mundus vult decipi
    Many people may find these results surprising, but there has actually been a steadily growing body of research on this link for the past 15 years. It's not a single study. There have been case controlled studies, longitudinal studies, and studies of those with and without psychosis disorders and their cannabis use before and after. There are decent, research-based reasons to suspect that marijuana is playing a causative role in triggering psychosis in some people.

    Gerhard Adam
    There are decent, research-based reasons to suspect that marijuana is playing a causative role in triggering psychosis in some people.
    ... and I'll bet there's as many that would link alcohol to psychosis, probably MSG for all I know.  That's the problem is that we already know that some percentage of the population will be susceptible to psychosis, even if they do nothing "wrong". 

    There needs to be a significantly higher correlation to establish the responsibility of cannabis in this, and more specifically any such study is worthless without a complete medical profile of ALL medications someone is taking and their interaction potentials.  That's why I know no worthwhile studies have been done, because such data is too difficult to get, and it's too subjective, so the researchers are picking and choosing their "proof".

    It's even more ridiculous when one considers that marijuana being illegal may lead to any number of other experimental drug scenarios, which are highly unlikely to have been reported, so the data is suspect right from its origins.  Has anyone ever ensure that cannabis was measured for THC content?  Interactions with amphetamines?  How about alcohol?  Perhaps cocaine?  Mescaline or LSD?  The point is I might as well ask for proof that the researchers could levitate their subjects, because none of that information is available at a sufficient level of detail to draw any kind of conclusion.
    Mundus vult decipi
    Two things come to mind, first stable well employed users are probably not in these studies, skewing the sample set. Second because it's illegal, and sold on the black market, by the same group who sells other illegal drugs, there may be a connection to other drug use, but it's more likely because it's illegal than anything else.

    While there will be issues with users, IMO it should all be legal, prohibition showed that while we do have to deal with alcoholics, we don't have to deal with machine gun toting moonshine runners, Like we do with illegal drugs now.
    Never is a long time.
    smells like selection bias. happy well adjusted smokers are quite likely to conceal use..given the current legal climate. A valid study would have a truly random sample from a representative slice of the populace. not sure how that would ne acheivanle with a volunteer study due to selfselection, .and a captive group i.e. prisoners athletes etc. would surely not be represemtative of thw whole population. Oh well, I have a feeling few.researchers are interested in a good study so much as getting the "right" result to please the corporation government or university funding the study. Do a drug study showing litle or no harm...then see if the NIH and DEA ever let you do one again. My college's BioChem dept. found out the hard way what happens to your sample license if you get the "wrong" answer. Then try to do a post hoc study of users and byebye funding.