Cause for double celebration this week with the publication of two new bits of research looking at cannabis and mental illness

The first casts further doubt on the links between cannabis use and and the development of mental illness. The study is called “Are cannabis use disorders associated with an earlier age at onset of psychosis? A study in first episode schizophrenia” by researchers at The Zucker Hillside Hospital of the North Shore Long Island in the USA – read the abstract here.

“Cannabis use disorders” is a term used by psychiatrists defined under a system known as Diagnostic and Statistical Manual of Mental Disorders (DSM) and we are now onto version IV. Strangely DSM-IV doesn’t seem to be online anywhere, but Cannabis use disorders are defined to be:

304.30 Cannabis Dependence
305.20 Cannabis Abuse

Cannabis dependence is a reasonably well understood term and can be paraphrased as existing when symptoms such as cannabis being used to the exclusion of other activities, using it greater amounts (tolerance), failing to stop even when the users desires to do so and so on. Cannabis abuse is defined broadly speaking as using cannabis in such a way as to cause problems for the user, such as causing problems at work, getting stoned when operating dangerous machinery (including driving) or when the use causes personal problems such as relationship issues.

So in plain English, the study looked at problem users. This is interesting because all the reports of cannabis leading to mental illness that caught the newspaper headlines a few years ago concerned just this sort of “problem user”. They were mostly if not all young adults – people in their early to mid teens – who seemed to hammer away at cannabis before developing a psychosis.

The purpose of this study is to determine if an earlier age at onset of positive symptoms in schizophrenia is associated with cannabis use disorders (CUD)

In other words to determine whether early use of cannabis did indeed appear to hasten the onset of psychotic illness. This of course is central to the claims made by RETHINK – the mental health charity which launched the “Cannabis and mental health” campaign, supported by Professor Robin Murray and others from the Maudsley Hospital in South London and so enthusiastically picked up by the rabid tabloid media and the prohibition campaigns. This is the issue the previous government used as the reason for reclassifying cannabis from class C to class B last year.

49 first-episode schizophrenia subjects with CUD were compared to 51 first-episode schizophrenia subjects with no substance use disorders for demographic and clinical variables.

So they had a sample size of 100, with 49 problematic cannabis users and 51 without any problematic substance use, which  admittedly isn’t huge, but the results were interesting none the less:

Although cannabis use precedes the onset of illness in most patients, there was no significant association between onset of illness and CUD that was not accounted for by demographic and clinical variables. Previous studies implicating CUD in the onset of schizophrenia may need to more comprehensively assess the relationship between CUD and schizophrenia, and take into account additional variables that we found associated with CUD.

Cannabis use disorders are associated with such issues as low educational achievement, worse socio-economic status and several other factors, but not the onset of psychotic illness. The final sentence there is actually quite cutting in its way – suggesting other studies which purport to show a connection between problematic cannabis use and the early onset of serious mental illness have looked at the association perhaps  rather narrowly.

The second study, also from the USA is called “Cannabis use disorders in schizophrenia: Effects on cognition and symptoms” – read the abstract here.

We retrospectively ascertained a large cohort (N=455) of SZ patients with either no history of a CUD (CUD-; N=280) or a history of CUD (CUD+; N=175).

So a bigger sample size here and the results are very interesting indeed:

Compared to the CUD- group the CUD+ group demonstrated significantly better performance on measures of processing speed (Trail Making Tests A and B), verbal fluency (animal naming) and verbal learning and memory (California Verbal Learning Test). Moreover, the CUD+ group had better GAF scores than the CUD group.

This defiantly counts as the “wrong” result:

Collectively, these findings suggest that SZ patients with comorbid CUD may represent a higher functioning subgroup of SZ. Future prospective studies are needed to elucidate the nature of this relationship.

So not only – according to these studies anyway – are problematic cannabis users not more likely to develop serious mental illness, but if they do it’s not going to be as bad. That simply isn’t what we’ve been lead to believe. Now of course there is the usual health warning – these are just two studies and they do not represent proof of anything, but for people worried about the claimed links between cannabis use and the development of mental illness they are at least encouraging results.

So does  cannabis protect against the development of mental illness? The authors don’t seem to think so. According to an article in Medwire news

The authors of the study do not, however, believe that cannabis improves cognition per se, but rather suggest that the CUD group has inherently better social skills, making them more likely to encounter the drug.

“Despite the controversy related to the causal relationship between CUD and schizophrenia, several lines of research suggest that patients with comorbid CUD may represent a clinically distinct subgroup of schizophrenia,” say Pamela DeRosse (The Zucker Hillside Hospital, Glen Oaks, New York, USA) and colleagues in the journal Schizophrenia Research.

So it’s Schizophrenia, but not as we know it? It is actually possible of course that the cannabis is having an effect on the development of the illness, CBD is known to have antipsychotic properties and THC is hardly claimed to be neutral.

There was one other side issue to come from these studies however, perhaps it’s a pedantic, trivial observation, perhaps not. These studies were based on “Cannabis use disorders” as defined by DSM-IV critieria. Wikipedia explains DSM:

The Diagnostic and Statistical Manual of Mental Disorders (DSM) is published by the American Psychiatric Association and provides a common language and standard criteria for the classification of mental disorders. It is used in the United States and in varying degrees around the world, by clinicians, researchers, psychiatric drug regulation agencies, health insurance companies, pharmaceutical companies and policy makers.

DSM-IV defines cannabis use disorders (plural) as mentioned above, essentially around the issue of dependence and problematic use. The important point is it isn’t a condition so much as a collection of symptoms grouped under a common heading; cannabis use isn’t a disorder. However, if you do a google for “cannabis use disorder” (singular) you come up with quite a few references to this apparent condition. One of the names which crops up rather prominently is one we’ve encountered before on this blog, that of Prof Jan Copeland who runs the Australian government funded anti cannabis campaign “Cannabis Information and Prevention Centre” a subject this blog covered a little while back. Way back in 2004 Jan Copeland published a paper called Developments in the Treatment of Cannabis Use Disorder: Interventions For Cannabis Use Disorder (Medscape) for example. What makes this interesting perhaps is that DSM-V is being put together now and it will contain a definition of  “Cannabis use disorder” – the draft is here. So what has happened is a collection of different and possibly unrelated symptoms is being collected together under one term after (and perhaps as a result of) it being used as a form of sloppy shorthand. One thing is for certain, the Daily Mail and its ilk  will love this, a medically defined condition caused by cannabis use is just what they want.