Something we’ve been waiting for ages for has finally arrived; the government has (albeit very quietly) published the study from Keele University entitled “Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005” (edit 2011 – read the full paper here)
Some 16 months back the Guardian ran an item about the proposed (as it was then) reclassification of cannabis to class B. Under the heading “Brown plans tougher line on cannabis against advice of own drug experts” the paper reported research carried out by a team from Keele University:
Their confidential paper found that between 1996 and 2005 there had been significant reductions in the incidence and prevalence of schizophrenia. From 2000 onwards there were also significant reductions in the prevalence of psychoses.
The authors say this data is “not consistent with the hypothesis that increasing cannabis use in earlier decades is associated with increasing schizophrenia or psychoses from the mid-1990s onwards.”
Note that last paragraph, we’ll come back to it shortly.
This was in April 2008, it is only now – on 26th June actually – the government has published this study and it hasn’t exactly gone out of its way to draw attention to it. UKCIA got wind of this not via the British media but from a tabloid style article from the US. The SFweekly.com site published this story under a Sun style headline:
Chronic City: After Further Review, Smoking Pot Doesn’t Make You Crazy — Blimey!
After a while the style settles down a bit
For the new study, British investigators at Keele University Medical School compared trends in cannabis use and instances of schizophrenia in the United Kingdom from 1996 to 2005. The research showed that even as marijuana use soared among the general population, “incidence and prevalence of schizophrenia and psychoses were either stable or declining” during this period.
The authors concluded that an expected rise in diagnoses of schizophrenia and psychoses did not occur over the decade under study. “This study does not therefore support the … link between cannabis use and incidence of psychotic disorders,” the study concludes, adding “This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence.”
Notice again the conclusion “This study does not therefore support the … link between cannabis use and incidence of psychotic disorders”. This seems to be a pretty well understood conclusion made by the Keele study.
A perhaps slightly more sober report came – again from the US – on the NORML blog. NORML is the American Legalise Cannabis Campaign known as the National Organisation for the reform of Marijuana Laws. Paul Armentano, NORML Deputy Director wrote on July 1st:
… a team of researchers at the Keele University Medical School have once and for all put the ‘pot-and-mental illness’ claims to the test. Writing in a forthcoming edition of the scientific journal Schizophrenia Research, they compare long-term trends in marijuana use and incidences of schizophrenia and/or psychoses in the United Kingdom. And what do they find?
The NORML blog then appears to quote the abstract from the Keele study as saying:
“[T]he expected rise in diagnoses of schizophrenia and psychoses did not occur over a 10 year period. This study does not therefore support the specific causal link between cannabis use and incidence of psychotic disorders. … This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence.”
Strangely this conclusion isn’t included in the Pubmed abstract the blog links to and neither is it included on the original hosted by Schizophrenia Research, who are publishing the actual paper. Has it been changed? This seems very odd.
Schizophrenia Research publish this abstract (as at 4th July anyway):
Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005
Martin Frishera Corresponding Author, Ilana Cromeb, Orsolina Martinoa, Peter Croftc
Received 17 April 2009; received in revised form 27 May 2009; accepted 30 May 2009. published online 29 June 2009.
A recent systematic review concluded that cannabis use increases risk of psychotic outcomes independently of confounding and transient intoxication effects. Furthermore, a model of the association between cannabis use and schizophrenia indicated that the incidence and prevalence of schizophrenia would increase from 1990 onwards. The model is based on three factors:
a) increased relative risk of psychotic outcomes for frequent cannabis users compared to those who have never used cannabis between 1.8 and 3.1,
b) a substantial rise in UK cannabis use from the mid-1970s and
c) elevated risk of 20 years from first use of cannabis.
This paper investigates whether this has occurred in the UK by examining trends in the annual prevalence and incidence of schizophrenia and psychoses, as measured by diagnosed cases from 1996 to 2005. Retrospective analysis of the General Practice Research Database (GPRD) was conducted for 183 practices in England, Wales, Scotland and Northern Ireland. The study cohort comprised almost 600,000 patients each year, representing approximately 2.3% of the UK population aged 16 to 44.
Between 1996 and 2005 the incidence and prevalence of schizophrenia and psychoses were either stable or declining. Explanations other than a genuine stability or decline were considered, but appeared less plausible. In conclusion, this study did not find any evidence of increasing schizophrenia or psychoses in the general population from 1996 to 2005.
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So it appears they are really not going out of their way to make this study and especially it’s conclusion public.I suspect had the conclusion been different it would have been splashed all over the tabloid press.
Thing is, this is dynamite evidence against the claims of a causal role for cannabis in the development of psychosis and frankly kills Reefer madness V2.0 stone dead. Why? Because simply this study covers the decade when both the both rates of cannabis use and the prevailance of so-called “skunk” were on the rise. If cannabis and especially the high THC versions had a causal role in the development of psychotic illness we would have seen an increase in those rates. Now, had the study found such an increase it would have supported although of course not proved the theory of a causal link between cannabis and mental illness. However, finding no increase (and indeed, perhaps even a decrease) provides a pretty definite conclusion: Cannabis does not cause psychotic illness.
Although it doesn’t actually say so in the abstract, the conclusion that “This study does not therefore support the specific causal link between cannabis use and incidence of psychotic disorders. … This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence.” is inescapably true.
Now this has a very important consequence for everyone in the UK, way beyond the single issue of cannabis and it’s ranking in the Misuse of drugs act. Our Prime Minister Mr Brown was made aware of this study before he made his decision to return cannabis to class B. As the Home Office put it to recently – as reported on this blog a few weeks ago:
The Frisher and Crome analysis of a fall of prevalence of diagnosed psychoses and fall of prevalence and annual incidence of diagnosed cases of schizophrenia and psychosis in general practice between 1996 and 2005, to which you refer in your letter, was reported by ACMD in its most recent report and was taken into account before coming to its conclusions on this issue.
So they saw the study and decided to ignore it. So we now have evidence like never before that the Prime Minister not only ignore the advice of experts, which is bad enough, but he actually ignores hard evidence when it doesn’t fit with his own prejudices. We knew this before, now we have evidence. This is serious and deeply worrying for the well being of the country, after all, if he did it with this issue he could do it with any.
The SFWeekly.com item mentioned above also mentioned another study which for some reason seems not to have grabbed the media’s attention.
Can recreational doses of THC produce significant dopamine release in the human striatum?
Stokes PR, Mehta MA, Curran HV, Breen G, Grasby PM.
Psychiatry Group, MRC Clinical Sciences Centre, Imperial College, Hammersmith Hospital Campus, Du Cane Road, London, W12 0NN, UK.
Cannabis use in early adolescence may be a risk factor for development of schizophrenia. In animals, Delta9-tetrahydrocannabinol (THC) increases the rate of dopamine neuronal firing and release in the striatum. Thus cannabis use may increase dopamine release in the human striatum leading to vulnerability to psychosis.
AIMS: To investigate whether THC, the main psychoactive component of cannabis, can produce dopamine release in the human striatum.
METHODS: Thirteen healthy volunteers, with previous cannabis experience, underwent two [11C]-raclopride positron emission tomography (PET) scans to indirectly measure striatal dopamine levels following either 10 mg THC or placebo.
RESULTS: Although THC markedly increased psychosis-like symptoms on the Psychotomimetic States Inventory (PSI), there was no significant effect of THC on [11C]-raclopride binding.
CONCLUSION: In the largest study of its kind so far, we have shown that recreational cannabis users do not release significant amounts of dopamine from an oral THC dose equivalent to a standard cannabis cigarette. This result challenges current models of striatal dopamine release as the mechanism mediating cannabis as risk factor for schizophrenia.
All this makes the claim by the home Office position reproduced on the Talk to Frank website that
The regular use of cannabis is known to be associated with an increase in the risk of later developing psychotic illnesses including schizophrenia.
Look simply wrong and no more than government anti drug propaganda.
In conclusion what this shows is that increased use of cannabis has not lead to an increase in the rates of the illness, so there can be no causal role for cannabis in the development of serious mental illness.This does not mean that unrestricted use by kids is OK, it’s not for a whole load of reasons to do with developing brains, learning ability and so on. It does mean the move back to B was done for the worst of all reasons – to satisfy the tabloid press and it does cast a doubt on the Prime Minister’s creditability.
It is also probably true that ill people are at risk from cannabis use and so need to be regarded as a vulnerable group deserving of special protection.