PSYCHOSIS, HYPE AND BALONEY

As the month began, the worldwide press jumped all over a study in the
March issue of the journal Addiction purporting to show a causal link
between marijuana use and psychosis. "Drug Doubles Mental Health Risk," the
BBC reported. "Marijuana Increases Risk of Psychosis," the Washington Times
chimed in.

Such purported links have lately become the darling of prohibitionists, but
a close look at the new study reveals gaping holes unmentioned in those
definitive-sounding headlines.

Before we look at the study itself, let's consider some basics: If X causes
Y, it's reasonable to expect a huge increase in X to cause at least a
modest increase in Y, but this has not been the case with marijuana and
psychosis. Private and government surveys have documented a massive
increase in marijuana use, particularly by young people, during the 1960s
and '70s, but no corresponding increase in psychosis was ever reported.
This strongly suggests that if marijuana use plays any role in triggering
psychosis, that effect is weak, rare, or both.

For this reason, researchers should approach "proof" that marijuana causes
serious mental illness with great caution. The researchers in this case, a
New Zealand team led by David M. Fergusson of the Christchurch School of
Medicine and Health Sciences, seem to have done just the reverse.

Fergusson's team looked at a group of 1,265 New Zealand kids who were
followed from birth to age 25 and assessed at various points along the way
for a variety of physical, mental and social problems and issues. At ages
18, 21 and 25 they were assessed for both marijuana use and supposed
psychotic symptoms. Having found a correlation with daily users reporting
the highest frequency of psychotic symptoms, they then applied a series of
mathematical models. These models are designed to adjust for possible
variables that might confound the results and to assess whether the
marijuana use caused the symptoms or vice versa.

Whatever model was applied, the correlation held up. But the reported
"growing evidence" that "regular use of cannabis may increase risks of
psychosis" depends completely on the validity of the underlying data, and
those data raise some screamingly obvious questions.

Psychotic symptoms were measured using 10 items from something called
Symptom Checklist 90. Participants were asked if they had certain ideas,
feelings or beliefs that commonly accompany psychotic states. The
researchers did not look at actual diagnoses, and the symptom checklist is
not identical to the formal diagnostic criteria listed in the DSM-IV
manual. Perhaps most important, they only used 10 "representative" items
from a much larger questionnaire.

These 10 items focus heavily on paranoid thoughts or feelings, such as
"feeling other people cannot be trusted," "feeling you are being watched or
talked about by others," "having ideas or beliefs that others do not
share." This presents a big methodological problem, because it is well
known that paranoid feelings are a fairly common effect of being high on
marijuana.

But the article gives no indication that respondents were asked to
distinguish between feelings experienced while high and feelings
experienced at other times. Thus, we are left with no indication at all as
to whether these supposed psychotic symptoms are long-term effects or
simply the normal, passing effects of marijuana intoxication. While it's
possible the researchers had these data and didn't see a need to report
them, the failure to do so is downright bizarre. It's like reporting that
people who go to bars are more erratic drivers than people who don't,
without bothering to look at whether they'd been drinking at the time their
driving skills were assessed.

Even if these were long-term effects, the researchers seem not to have
considered that what might be an indication of psychosis in other
circumstances could be an entirely normal reaction for people who use
marijuana. Consider: Someone using a substance that is both illegal and
socially frowned-upon almost by definition has "ideas or beliefs that
others do not share." This is not a sign of mental illness. It's a sign of
a rational person realistically assessing his or her situation.

The same goes for "feeling other people cannot be trusted." Just ask Robin
Prosser, the Montana medical marijuana patient arrested last summer on
possession charges by the cops who came to save her life after she'd
attempted suicide because she was in unbearable pain after running out of
medicine.

Fergusson reports very little raw data, so we don't know which symptoms
came up most often, or whether the differences in average levels of
symptoms between users and non-users came from a few people having a lot of
symptoms or a lot of people having a couple symptoms. The heavy-user group,
with the highest levels of supposed psychosis, reported an average of less
than two symptoms each. So it is entirely possible that the entire case for
marijuana "causing" psychosis is based on marijuana smokers having the
completely reasonable feelings that they have beliefs different from
mainstream society and thus should be a tad suspicious of others.

"Proof" that marijuana makes you psychotic? No. Not even close. But don't
expect the mainstream media to figure this out.