The BBC took a step forward this week producing a balanced reviewrb editors selection Cannabis: What The BBC Forgot to Tell You of the literature on cannabis for the first time in about a decade. There are however two myths about cannabis that the documentary fails to really break down.

1. Cannabis Causes Schizophrenia

Schizophrenia rates have been at a plateau for the last 100 years (consistently affecting about half a percentage point of the population). The majority of schizophrenics have never used cannabis in their life. Schizophrenia appears to be a genetic disorder, passing down family lines.  In the past thirty years cannabis use has exploded, rising between ten and twenty fold (in the US now overtaking cigarette use in young people). In the same period of time the government has restricted the market resulting in a boom in skunk production over the past decade. With both of these two factors, if the hypothesis that cannabis causes schizophrenia were true we would expect to see a rise in schizophrenia. This did not happen, in fact there is some evidence schizophrenia is in decline. Therefore it appears clear there is no direct causal link between cannabis and schizophrenia. For a reference point, in the same period alcohol use has doubled and liver disease has risen two fold becoming the only form of “death” that is on the rise by any great degree.

Growth in Liver Disease Correlates Perfectly with Growth of Alcohol Consumption

liver disease1 Cannabis: What The BBC Forgot to Tell You

This does beg the question of why there is a slight correlation between people with schizophrenia and cannabis use. It is starting to look more likely that cannabis is used by people with schizophrenia attempting to self medicate. One component of cannabis (CBD) has even been found to be an effective anti-psychotic. Ironically, this is the component that is lost when growers are forced to farm intensively indoors (i.e. in skunk). The evidence is certainly clear however that the main component in skunk varieties (THC) has a negative effect on those with schizophrenia, however schizophrenics are still attracted to skunk because of it’s anxiety relieving properties. The conclusion of the BBC program that it is safest to stick to strains with balanced levels of CBD/THC such as Thai Stick and avoid if your family has a history of mental illness certainly seems to be correct.

*For the record, 90% of schizophrenics smoke cigarettes for the same reasons. No one however is suggesting cigarettes cause schizophrenia.

2. Cannabis is Addictive

To it’s credit, the program does note that cannabis is not physically addictive and there are no physical withdrawal symptoms. However it naively states that “treatment rates for cannabis are on the rise” failing to recognise the proportion of those in treatment forced to attend “rehab” centres by court order instead of going to jail for possession/dealing. This is really not a fair measure of harm. I’ve been unable to uncover rehab admission statistics broken down by mode of admission, the NHS stats leave that key component out (if anyone has access please do send). It seems pretty inappropriate to force cannabis users to attend these classes when there are endless waiting lists for serious drug addicts.

Other than those two points the program was fair and balanced and I’d recommend it. In other news, across the pond the US National Institute of Drug Abuse (NIDA) has just started claiming cannabis use causes testicular cancer based on one tiny study that really showed no such thing. Sigh.

Hickman M, Vickerman P, Macleod J, Kirkbride J, & Jones PB (2007). Cannabis and schizophrenia: model projections of the impact of the rise in cannabis use on historical and future trends in schizophrenia in England and Wales. Addiction (Abingdon, England), 102 (4), 597-606 PMID: 17362293

Zuardi, A., Crippa, J., Hallak, J., Moreira, F., & Guimarães, F. (2006). Cannabidiol, a Cannabis sativa constituent, as an antipsychotic drug Brazilian Journal of Medical and Biological Research, 39 (4) DOI: 10.1590/S0100-879X2006000400001

GREEN, B. (2005). Cannabis use and misuse prevalence among people with psychosis The British Journal of Psychiatry, 187 (4), 306-313 DOI: 10.1192/bjp.187.4.306

Cattapan-Ludewig K, Ludewig S, Jaquenoud Sirot E, Etzensberger M, & Hasler F (2005). [Why do schizophrenic patients smoke?]. Der Nervenarzt, 76 (3), 287-94 PMID: 15448920

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  • Johan

    Excellent post, thanks! Keep up the good work!

  • edviges

    they also mention smoking cannabis increases the risk of having a heart attack , do you know anything about this?

    thank you

    • Neurobonkers

      Yes, unfortunately smoking anything raises risk of heart problems substantially. This problem can be largely avoided by using a “vaporiser” which heats the plant to the level at which the active ingredient (THC/CBD) can be inhaled as vapour but before which the matter combusts. This drastically reduces the level of tar and carbon monoxide in the smoke but some do still report some respiratory problems. Some studies have also reported that vaporising can increase the levels of THC transmitted.

      Alternatively using the herb to make cakes alleviates this problem entirely.

  • Nathan

    Cannabis is not addictive, you cannot overdose on it, there are no symptoms of withdrawal. It does not lead to violence or sexual promiscuity. It’s effective at reducing anxiety and treating pain. It’s illegal because of a series of poorly crafted lies. I thought I’d heard them all, but conflating cannabis use with schizophrenia? I think If I heard of this outside of the context of refuting it I would seriously lose my shit.

  • Anonymous


  • Peter Reynolds

    Excellent post. Well done.

    Please join the LCA. The cananbis campaign is about to be re-launched in Britain.

  • Jules

    Looking at the graph, it would appear to show that the increase in cannabis consumption is causing a decrease in cancer deaths.

    Keep up the good work!

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  • Tom

    Articles like this need more media coverage.

    Great stuff!


  • Smokey & the bandit

    Great post, very well pointed out and to anyone who looks past the crap of the media, very easily seen.

    As for LCA, wouldn’t touch them with a barge pole…the likes of win and co on there has ruined it.

  • Neuroskeptic

    Good post. There is however a bit more to it than this…

    It seems unlikely to me that cannabis causes schizophrenia. As you say, rates of schizophrenia aren’t rising.

    Whether it causes psychosis however, is a different question. You can be psychotic without being schizophrenic, and many people are. You can even be schizophrenic without ever being psychotic although that’s extremely rare and arguably not schizophrenia at all.

    To get a diagnosis of schizophrenia you need symptoms for at least 6 months, but a lot of people become psychotic for a few days or weeks, and then recover, avoiding a diagnosis of schizophrenia. Also, I think psychiatrists try to avoid that diagnosis whenever possible because it’s seen as “the worst psychiatric illness”.

    It might well not cause psychosis either, but I think that’s an open question.

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  • shane

    Not addictive? Not so sure… heavy use for a while can [produce strong withdrawal symptoms for some. My dad is unbeleivably edgy if he goes 2 days without it. I quit months ago, and i’m only just over the insomnia.

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  • Jambo

    As a practising psychiatrist for many years, I think you are mistaken. The diagnosis of schizophrenia is imprecise, and a slight change in criteria can alter the rates. Also, for most psychiatrists, if the psychosis- acute or chronic – is caused by cannabis that would rule out the diagnosis of schizophrenia completely. Therefore no reliance can be placed in a causative analysis of schizophrenia from rates of illness and cannabis use.

    What is striking to me, and supported by research, is the number of chronic psychoses coinciding with the commencement of cannabis use at a young, pre-adolescent age. There is a speculative mechanism linking the cannabis receptors on neuroglia, and neuroglia’s role in the cortical apoptosis that takes place in adolescence up to the age of 23 to 25.

    With regard to addiction, it is a complete nonsense to say that it is not addictive. Addiction is a state of mind, not chemical withdrawal. It is common place in psychiatry to see patients who centre their whole life around getting cannabis from the moment they get up until they got to bed, and that can include promulgating literature about it’s lack of harm.

    • Neurobonkers

      I accept your point on the definition of Schizophrenia, however to date I’ve seen no evidence that anything but extremely excessive use at a young age could be considered a causal factor even if we widen the net to include all forms of psychosis. It stands to reason that it is not a causal factor in the vast majority of the population due to the millions who use it without ever experiencing problems.

      I do agree with you on the point about children. I would certainly never allow children to use it and in my opinion this is by far the biggest danger of the drug after the legal threat. This issue can never be tackled without regulation.

      I would disagree on the issue of addiction. Physical addiction is guaranteed and severe with drugs such as opiates which are widely prescribed to treat chronic pain. For the vast majority of cannabis users there is little or no psychological addiction and physical addiction has never been proven. By any measure you are less likely to risk addiction using cannabis than most heavy duty painkillers which normally also have side effects that cannabis does not. Yes it is the case that a statistically minuscule percentage of cannabis users become psychologically dependent in the same way that people can be addicted to chocolate, sex and gambling. It would be far more appropriate to keep the addiction centres which are chronically oversubscribed for use only by these few people and addicts of physically addictive drugs. Currently this can not happen because that money is spent on sessions for non-problem cannabis users who have been caught and are given the choice of “treatment” or jail.

      • Jambo

        There is a need for clarity over the use of the label addiction. Rats will not “work” to get cannabis stimulating the pleasure pathways e.g. MFB, in contrast to drugs such as caanabis, opiates, etc.. However as one of your commenters illustrated there are physical withdrawal effects on stopping regular cannabis use, e.g. insomnia. And many people are addicted to cannabis in that they will neglect basic drives and behaviours to obtain the drug, and this generalises to other cannabis-linked behaviours.

        It is very difficult to get reliable statistics on illegal activities. But I, like many psychiatrists see many patients who have used cannabis regularly from a very young age, who are strongly addicted to it. We also meet many distraught relatives whose child’s emotional and intellectual development has halted. The picture is very similar to that of alcohol.

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