INTERPRETING HAZY WARNINGS ABOUT POT AND MENTAL ILLNESS

Smoking pot won't make you crazy, but trying to find the truth behind
the recent rash of headlines regarding a supposed link between
cannabis and mental illness might.

According to the Associated Press and other news sources, a new study
in the British medical journal The Lancet reports that smoking
cannabis -- even occasionally -- can increase one's risk of becoming
psychotic. It sounds alarming at first, but a closer look at the
evidence reveals that there's less here than the headlines imply.

First, there is no new study. The paper published in The Lancet is a
meta-analysis -- a summary of seven studies that previously appeared
in other journals, including some that were published decades ago.
Second, the touted association between cannabis and mental illness is
small--about the same size as the link between head injury and
psychosis. Finally, despite what some new sources suggest, this
association is hardly proof of a cause-and-effect relationship between
cannabis and psychosis,

So why the sudden fuss?

Part of the answer is political. The recently elected Conservative
British government longs to stiffen penalties against marijuana users.
One way to justify this move involves convincing the public that The
Lancet proved that puffing the weed will make you batty. Of course,
that's not what the article says at all.

In fact, investigators actually reported that cannabis use was
associated with a slight increase in psychotic outcomes. However, the
authors emphasized (even if many in the media did not) that this small
association does not reflect a causal relationship. Folks with
psychoses use all intoxicants more often than other people do,
including alcohol and tobacco.

Cannabis use can correlate with mental illness for many reasons.
People often turn to cannabis to alleviate the symptoms of distress. A
recent study performed in Germany showed that cannabis offsets certain
cognitive declines in schizophrenic patients. Another study shows that
psychotic symptoms predict later use of cannabis, suggesting that
people might turn to the plant for help rather than become ill after
use.

Perhaps the most impressive evidence against the cause-and-effect
relationship concerns the unvarying rate of psychoses across different
eras and different countries. People are no more likely to be
psychotic in Canada or the United States (two nations where large
percentages of citizens use cannabis) than they are in Sweden or Japan
(where self-reported marijuana use is extremely low). Even after the
enormous popularity of cannabis in the 1960s and 1970s, rates of
psychotic disorders haven't increased.

Despite this evidence, we'd like to spread the word that cannabis is
not for everybody. Teens should avoid the plant. Folks with a
predisposition for mental illness should stay away, too. This
potential for health risks in a few people, however, does not justify
criminal prohibitions for everyone. (We wouldn't pass blanket
prohibitions against alcohol simply to protect pregnant women, for
example.) The underground market does an extremely poor job of keeping
marijuana out of the hands of teens and others who should stay away
from it. A regulated market could better educate users to potential
risks and prohibit sales to young people.

Consequently, the review in The Lancet suggests that if cannabis
really does alter risk for mental illness, we can't leave control of
sales to folks who are willing to break the law. Instead, a taxed,
regulated, age-restricted market is our best chance to keep any
negative consequences of marijuana under control.