28/07/2007 00:00:00
NORML: Pot Use Doesn't Exacerbate Symptoms of Schizophrenia, Study
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What cannabis / psychosis link?
I was planning on busting out a quick response to the recent news of an
apparent cannabis / psychosis link, noting that meta-analysis is fraught
with peril - in fact, the last round of Ecstasy toxicity scare stories
were based on a flawed meta-analysis. But our own Omgoleus noted in a
comment to the last post:
Note that the only thing new here is a meta-analysis, where researchers
(possibly feeling lazy) go over the results of all the previous studies
in a field to see what they say collectively, rather than doing any new
work.
This has the effect of improving statistical power (because you
effectively have a big new sample composed of all the people in all the
studies) but most definitely does NOT solve any methodological problems
or limitations of the original study.
So, if there were any biases in the original studies, the biases are
still there in the meta-analysis. Caveat emptor, as the
somewhat-misapplied saying goes.
It's not just that they round up old studies and attempt to come up with
new conclusions. It's that they can also pick and choose which studies
to include, thus skewing the conclusion toward whatever bias they might
have, which clearly happened in the past. Now I'm not saying that's what
happened this time, although the article does note the meta-analysis did
exclude subjects who were already showing signs of psychosis at the
start of the studies in question. But without examining the entirety of
the literature, it's hard to say. Luckily for us, Dominic Holden over at
the SLOG has already dug a little deeper, and noted:
By reading these headlines, you would believe recent findings show
conclusive evidence that marijuana use leads to increased risk of
psychoses. You would be wrong. The report is actually based on a
meta-analysis of previously debunked studies, and the findings, as the
article’s text immediately volunteers, are completely ambiguous.
Indeed, take a look at this very recent study, via a link that Holden
provided:
Marijuana use is not associated with heightened symptoms of
schizophrenia, according to data to be published in the journal
Schizophrenia Research.
Investigators at London’s Institute of Psychiatry assessed whether the
prior use of cannabis in patients with schizophrenia was associated with
appreciable changes in schizophrenic symptoms compared with patients who
had no history of marijuana use. Researchers performed logistic
regression analysis on 757 volunteers with cases of first onset
schizophrenia. Of these, 182 (24 percent) had reportedly used cannabis
in the year prior to diagnosis, while 552 (73 percent) had not. (The
remaining three percent had no data available.)
Investigators reported no statistically significant "differences in
syptomatology between schizophrenic patients who were or were not
cannabis users" after controlling for patients’ age, sex, and ethnicity.
Researchers also failed to find "any evidence that cannabis users with
schizophrenia were more likely to have a family member with the disorder."
These findings "argue against a distinct schizophrenic-like psychosis
caused by cannabis," authors concluded.
The study is the largest trial ever conducted to compare cannabis using
and non-using schizophrenic patients, investigators said.
What seems to be clear is that:
Although investigators did not assess whether cannabis consumers had
greater odds of contracting schizophrenia compared to those who did not
have a history of smoking pot, prior reviews have downplayed such an
association. Most recently, Britain's Advisory Council on the Misuse of
Drugs (ACMD) concluded in 2006, "For individuals, the current evidence
suggests, at worst, that using cannabis increases lifetime risk of
developing schizophrenia by one percent."
A separate 2006 report by Britain’s Beckley Foundation speculated that
cannabis may "precipitate schizophrenia in people who are already
vulnerable" to the disease, but it also acknowledged that the "increased
rates of cannabis use in the last thirty years have not been accompanied
by a corresponding increase in the rate of psychosis in the population."
Even the authors of the meta-analysis under critique here are clear that:
There could be something else about marijuana users, “like their
tendency to use other drugs or certain personality traits, that could be
causing the psychoses,” Zammit said.
And finally, as Holden points out:
Is this not obvious? If this study shows anything, it’s that psychotics
are smoking pot to chill the £!!£ out.
But it's not clear that this does study does show anything, without
carefully examining all "35 studies on the long-term effects of cannabis
use in Europe, the US and Australasia" to determine if, as Omgoleus
describes above, any of these studies have "methodological problems or
limitations," the most common of which in studies like this is the
inability to control for any other kind of drug use or environmental
issue that may have an impact on a person's mental state. Given that
subjects in these studies are typically self-reporting users of illicit
substances (i.e., no one is taking a pool of subjects off into a private
facility, and then dosing them with medical-grade marijuana and nothing
else), these studies are very difficult to take at face value.
That said, if anyone out there actually has read these same 35 studies -
while at the same time examining the literature to make sure any studies
that don't support the meta-analysis (like, oh, gee, the one that Holden
pointed us to) weren't excluded - feel free to ping us with your thoughts.
NORML: Pot Use Doesn’t Exacerbate Symptoms Of Schizophrenia, Study Says
www.dosenation.com/listing.php?id=2813
Source:
http://www.ukcia.org/news/shownewsarticle.php?articleid=12750
Author:
DoseNation.com via UKCIA
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