At least according to a recent study done by the British Medical Journal (BMJ 2011; 342:d738)
Results In individuals who had no reported lifetime psychotic symptoms and no reported lifetime cannabis use at baseline, incident cannabis use over the period from baseline to T2 increased the risk of later incident psychotic symptoms over the period from T2 to T3 (adjusted odds ratio 1.9, 95% confidence interval 1.1 to 3.1; P=0.021). Furthermore, continued use of cannabis increased the risk of persistent psychotic symptoms over the period from T2 to T3 (2.2, 1.2 to 4.2; P=0.016). The incidence rate of psychotic symptoms over the period from baseline to T2 was 31% (152) in exposed individuals versus 20% (284) in non-exposed individuals; over the period from T2 to T3 these rates were 14% (108) and 8% (49), respectively.
I recently ran across a totalitarian fascist trumpeting this study as a reason to keep marijuana illegal. So I figured I’d point out some obvious problems with it.
First we have to understand exactly what the authors mean when they use the word psychosis. Psychosis is a very generalized term that covers everything from auditory hallucinations to out-of-body experiences.
Wiki describes it thusly:
Psychosis is an abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a “loss of contact with reality”.
People experiencing psychosis may report hallucinations or delusional beliefs, and may exhibit personality changes and thought disorder. Depending on its severity, this may be accompanied by unusual or bizarre behavior, as well as difficulty with social interaction and impairment in carrying out the daily life activities.
A wide variety of central nervous system diseases, from both external poisons and internal physiologic illness, can produce symptoms of psychosis
Given that pot induces altered mental states, and that a heavy dose can cause mild hallucinatory effects or paranoia during the period of being high, a distinction must be made between a persistent psychosis that is the result of a true mental disorder and “incident psychotic symptoms” (ie. something that could happen as a normal and expected result of being high).
The study concludes:
Psychotic experiences are a common and generally transitory phenomenon in the general population, that, nevertheless, might become abnormally persistent and progress to clinical psychotic disorder if combined with exposure to environmental risks. Our study confirmed cannabis as an environmental risk factor, impacting on risk of psychosis by increasing the risk of incident psychotic experiences, and, if use continues over time, increasing the risk of persistent psychotic experiences.
The finding that longer exposure to cannabis was associated with greater risk for persistence of psychotic experiences is in line with an earlier study showing that continued cannabis use over time increases the risk for psychosis in a dose-response fashion. This is also in agreement with the hypothesis that a process of sensitisation might underlie emergence and persistence of psychotic experiences as an indicator of liability to psychotic disorder [such as schizophrenia].
So what they are saying is essentially that – oh look, people who get high experience a higher rate of “incident psychosis” (well no kidding), and that if they keep smoking pot they’ll keep experiencing incidents of psychosis (duh), which means it must be persistent psychosis! – And because they are experiencing persistent incidences of psychosis, we can say they have a liability towards acquiring a real psychotic disorder.
Take some time and think about how that conclusion was phrased and what they mean when they use the term psychosis and you’ll see that basically they are highlighting the obvious (people who smoke pot occasionally have a high that causes some mild hallucinations or detachment from reality) and then they are inferring that because of this, those people are at risk of developing a psychotic disorder that is a real mental health issue.
I would say that is more like jumping to conclusions.
A much more simple method of determining if smoking pot raises the risk of developing a psychotic disorder is to look a the changing rates of pot usage over an entire population and compare that to the number of reported cases of psychotic disorders. It stands to reason that if smoking pot actually increases your chance of developing a psychotic disorder, then if the number of pot smokers increases, so too should the number of people developing schizophrenia.
So what do scientists find when they do that?
The prediction of the hypothesis that cannabis causes psychosis was not supported by the data on trends in the incidence of psychosis. There was no evidence that there has been an increase in the incidence of psychosis over the past thirty years of the magnitude predicted by the hypothesis. This suggests that cannabis use does not cause cases of psychosis that would not otherwise have occurred.
One further point was clear. Even if regular cannabis use did double the risk of users developing schizophrenia (the “doubling” of risk being our best current estimate), it would be unlikely that there would be a large change in the population prevalence of schizophrenia. Even if every person in the general population used cannabis weekly, and cannabis use doubled the risk of psychosis, the prevalence of schizophrenia in the general population would increase from 1% to 2%. This does put in context the extent of the possible problem on a population level.
However, an increase of 1,000 cases per birth cohort – as was produced by modelling here - would almost certainly have been remarked upon in clinical settings. The widespread discussion ofapparent declines in the incidence of schizophrenia suggests that this hasn’t occurred. Even if some of 31the environmental risk factors for schizophrenia have been reduced, such as poor maternalnutrition, infectious disease, and poor antenatal and perinatal care (Eagles, 1991; Takei et al., 1996), it seems unlikely that the decline in incidence would have exactly offset the increases of 1,000 incident cases per birth cohort predicted by the hypothesis that cannabis causes schizophrenia.
Clearly pot smokers pose a serious and imminent threat to society.
We must keep pot banned for the safety of our children!
Now you’ll have to excuse me while I down a bottle of 5-hour ENERGY® so I’m alert enough to drive to the liquor store to pick up a 40 oz. Mickey’s Fine Malt Liquor® and a pack of Marlboro Reds®. While I’m there I might also grab a bottle of Super Glue® and perhaps a few cans of Dust Off®.
In other news:
Alan Johnson, the home secretary, has sacked Professor David Nutt as senior drugs adviser after the scientist renewed his criticism of the government’s decision to toughen the law on cannabis.
The decision follows the publication of a paper by the Centre for Crime and Justice at King’s College London, based on a lecture Nutt delivered in July. He repeated his familiar view that illicit drugs should be classified according to the actual evidence of the harm they cause and pointed out that alcohol and tobacco caused more harm than LSD, ecstasy and cannabis.
He also argued that smoking cannabis created only a “relatively small risk” of psychotic illness.