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Reefer madness?


A report from the Netherlands (here) suggests that smoking marijuana does not cause schizophrenia. Epidemiologists invariably uncover a high correlation between incidence of smoking marijuana and acquisition of schizophrenia. But, according to the report:

“The scientists say the drug only seems to affect people who are genetically predisposed to getting schizophrenia (meaning they will get it anyway). As schizophrenia manifests itself during adolescence, and many people start taking cannabis during adolescence – it is just coincidence that some people develop the mental illness soon after they start taking the drug. The authors of the report wrote It is therefore advisable that youngsters with a family history of schizophrenia and patients with a schizophrenic disorder be discouraged from using cannabis”.

A number of recent studies have suggested to the contrary that is does cause such problems (see here and here) although the results cited are confirmed in an important Australian study here. This latter study did suggest that use of marijuana might tip those predisposed into full-blown psychosis and might worsen problems among those already suffering from the disease. In addition later studies confirm higher levels of depression among youth using marijuana.

This is an important Australian health policy issue. The recent 2004 National Drug Survey shows that 21% of those aged 14+ had been offered marijuana in the previous 12 months and that, at some stage in their life, 34% had used it. But there is increasing community concern over marijuana use with 29% regarding it as a ‘problem’ drug in 2004 compared to 24% in 2001. This increase reflects the perception that marijuana use causes psychosis.

In South Australia, possession of marijuana has been decriminalised – possession of less than 25 grams results in a fine of $50 which, if paid, avoids a criminal conviction. In other states such as NSW there are moves to strengthen penalties against use (here). The Federal Government is currently engaged in an intensified campaign to further limit marijuana use and to reverse decriminalisations that have occurred in the ACT and South Australia (here).

My own view is that given the mixed evidence use of marijuana is not a good idea particularly if you are a teenager. There is growing evidence that, even apart from fears of inducing schitzophrenia, use by teenagers delays their cognitive development. According to a recent report:

“There is evidence that individuals who start to smoke marijuana at an early age – while the brain is still developing- show greater cognitive deficits than do individuals who begin use of the drug when they are older, but the reasons for this difference are unclear.

Scientists from the Harvard Medical School and from the intramural research program of the National Institute on Drug Abuse (NIDA) found lasting cognitive deficits in those who started to smoke marijuana before age 17. The researchers analyzed neuropsychological test results from 122 long-term heavy users of marijuana and 87 subjects who had used marijuana only a few times (control subjects). Sixty-nine of the 122 users started using marijuana at age 17 or before. The subjects were between the ages of 30 and 55 at the time of the study, and all had refrained from any drug use 28 days prior to testing.

Individuals who started using marijuana at age 17 or younger performed significantly worse on the tests assessing verbal functions such as verbal IQ and memory of word lists than did those who started using marijuana later in life or who had used the drug sparingly. There were virtually no differences in test results among the individuals who started marijuana use after age 17 and the control subjects”.

After attending a number of recent neuroscience seminars on the effects of marijuana I think these concerns have a reasonably high probability of being correct. Moreover, teenagers have high discount rates and levels of impulsiveness. I therefore reject liberal approaches to reform marijuana law (particularly among youth) and support laws that will induce cautious behavior.

9 comments to Reefer madness?

  • MIke Hart

    HC, frankly I think you wrong about the continued issue of controls on marijuana for reasons concerned with its use as a recreational euphoriant. The study as usual has a miniscule sample, poor controls and ignores like most the standout data, used or have used, extrapolation does not hold. This is a predictable outcome for research and political discussion dealing with alleged psychological harm. On the numbers hardly a public health crisis!

    You should read Lupiens 1995 MA thesis ‘Unravelling an American Dilemma: The demonisation of Marijuan’. Credible and looks at debate from an economic perspective. A remarkably useful agricultural product, for paper, oils for polymers, pharmacologically and as a general oil. Per acre produces the equivalent of 40 of forest in paper pulp, plus oils. Rate of regrowth 1 to 60 comparitive. The restrictions are simply economic madness. The personal use is a simple manageable issue.

    Equally importantly we currently spend probably close to several hundred million dollars in law enforcement annually on marijuana prohibition with no change to the percentages of current or former users, so the market is enforcement inelastic. The cost in terms of police corruption and the waste of court time and legal facilities simply stupendous.

    Craziest bit of feel good politics I have seen or will see, simple folly.

  • hc

    I think the neuroscience of marijuana use is of concern. The evidence is not clearcut but substantial numbers of cannibis are presenting themselves to clinics for treatment as addicts who undergo withdrawal when cannabis use ceases. There is a strong correlation with psychiatric disorders, that does not prove causation, but which is so strong it cannot be ignored. See e.g. G.F. Koob & M. Le Moal, The Neurobiology of Addiction, Academic Press, 2006.

    Mike, I am not a right-wing nut who drinks whisky while lecturing on the dangers of marijuana. I grew into adolescence in Sydney in the 1960s/1970s and all my friends smoked the stuff. In my view then it was less harmful than having a beer. Having read the literature I am unsure now.

    The dangerous bit is the claimed particular dangers of smoking marijuana (and indeed cigarettes) during adolescence. The brain takes a long timne to develop completely – it may continue developing past age 20 – and there are reasonable concerns that cognitive development may be impaired by using cannabis.

  • Robert Merkel

    If you’re going to make the case against decriminalization on the basis that it increases teenage usage, do you have any evidence to support this contention?

  • Sam Ward

    What Robert said. Marijuana is fairly unique in that it can be grown in your backyard and requires very little preparation once grown.

    No amount of law enforcement effort will ever stop teenagers from smoking marijuana, so why do we bother wasting all that money?

  • hc

    Robert.

    I think decriminalisation would be disasterous. Participation elasticities quite high and I think prices would fall quite a bit. The evidence fairly uniform I think throughout the literature.

    And to Sam, I am not opposed to teenagers getting high per se. But there is weak evidence of connection with inducing psychosis, stronger evidence of worsening a pre-existing condition and reasonably strong evidence of aggrevating depression.

    The neuroscientific unknowns are compelling for me. There are significanrt effects of cannabis on brain and it seems particularly strong effects among youth.

    It surprises me that many people presenting themselves at drug treatment clinics have problems with cannabis. It surprises me but it is a fact.

  • Mike Hart

    HC, I do not disagree that any study can eventually find some negative about psychotropic drugs, the chemistry of the brain is still poorly understood, however I am not satisfied with the data or the study groups on a heuristic basis. I am quite prepared to state that I can see nothing wrong with people altering their minds or body chemistry in any way they choose, if it is done responsibly, that is, without harm to another. I take issue with the policy of prohibition based on the protestant work ethic as a value base.

    I spent a long time in analysis and law enforcement and particular corruption, a economic dissection of the issues vis a vis cost benefit analysis produces a quite different result as far as I am concerned. I have seen no credible paper in twenty years from anyone proposing prohibition that does not derive from a hidden assumption that people should not enjoy themselves when we don’t or the more facile, ‘but its illegal’proposition.

    I agree that there probably is some deliterious effects on young brains, but then its the same with any other stimulant or drug (alcohol, tobacco etc.)We all know that lots of substances can do us harm but used in a measured way minimise harm and allow us to function succesfully.

    The only outcome from all the past decades of prohibition that I have ever seen is stable consumption rates ove time, equally stable and relatively declining prices (so much for market intervention using law enforcement)and bloated allocations to law enforcement of all persuasions to continue the same old tired interdiction policies, increasing gaol populations and continued corruption of police and others. The argument about increased potency is a furphy as well in my view engineered by the SA Police who were vehemently oppposed to the decriminalistion policy (aided and abetted by their more rabid counterparts in other police forces). I have had a look at the data and the THC content increase is basically minisucule, you can get the same variability over time with normal agricultural seasons.

    I simply think the money is better spent not interfering in peoples private lives, not on bloated incompetent police bureaucracies and even a small diversion of the sums involved into practical health management programs would have far more benefit than the time wasted in courts, legal proceedings and maintaining custodial facilities.

    But then I am probably an unreconstructed hippie anyway.

  • hc

    Mike. There are two issues (i) whether harm is caused and (ii) whether policies that penalise use work. On (i) I don’t think we differ much – there could be a problem and you are right, the neuroscience is not all in. I am cautious and suggest a case for not using. On (ii) I disagree. I think restrictive policies against some drugs (e.g. the supply restrictions on heroin use limited usage significantly with substantial ongoing effects – the so-called ‘heroin drought’ of 2001 being a consequence.

    I think demand for drugs depends on various user costs and that penalties and price have an impact.

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