JOURNAL ARTICLES LINK MARIJUANA TO SCHIZOPHRENIA

A pair of articles in the Canadian Journal of Psychiatry has
resurrected the "reefer madness" argument about marijuana and its
links to mental illness.

Cannabis use can trigger schizophrenia in people already vulnerable to
the mental illness -- and this fact should shape marijuana policy,
argue two psychiatric epidemiologists in this month's journal.

The link between marijuana use and schizophrenia is generally accepted
in the psychiatric community. The problem is that the vulnerable
population -- mostly teenagers -- generally isn't eager to absorb the
message.

Australian epidemiologists Louisa Degenhardt and Wayne Hall reviewed
eight international studies of teens and young adults that examined
the link between marijuana use and schizophrenia. They concluded using
marijuana can precipitate schizophrenia in users who have a personal
or family history of schizophrenia.

One 15-year study of 50,000 young people in Sweden, for example, found
those who had tried marijuana by the time they were 18 were 2.4 times
more likely to receive a diagnosis of schizophrenia. The Swedish
researchers concluded that 13 per cent of schizophrenia cases could be
averted if all cannabis use was prevented.

Another study of almost 5,000 subjects in the Netherlands replicated
the findings, and also found that marijuana users were more likely to
be diagnosed with schizophrenia during the study's three-year
follow-up period. Other studies suggested that subjects who used
marijuana in their early teens were more likely to be diagnosed with
schizophrenia by their mid-20s.

In a companion article, Hall and Degenhardt argue the evidence has
policy implications. Young people should be warned of the
marijuana-schizophrenia link, since most schizophrenics are diagnosed
by their late teens, about the same time teens are experimenting with
cannabis.

The link has been used to argue in favour of recriminalizing marijuana
in some Australian states. However, only one per cent of the
population will be diagnosed with schizophrenia in their lifetimes.

Hall, a researcher at the University of New South Wales in Australia,
said it's a tricky argument to make when, by the numbers, marijuana
will adversely affect so few people. But he points out schizophrenia
has a high personal and economic cost.

Although it's unlikely that a vulnerable person will develop the
illness after puffing on a single joint, Hall said some studies
suggest marijuana smokers are two or three times more likely to be
diagnosed with schizophrenia. In Australia -- where marijuana use is
heavy among teens -- it's not uncommon for 20 to 30 per cent of new
episodes of schizophrenia to be among patients who use marijuana daily
or almost daily.

"There are a lot of other reasons to discourage young people from
using cannabis," said Hall, who believes that young people should know
about the link and also be on the lookout for schizophrenic symptoms
that show up among their friends who smoke marijuana.

Wende Wood, a psychiatric pharmacist at the Toronto-based Centre for
Addiction and Mental Health said people who want to smoke marijuana
should wait until they are at least 25. The human brain had developed
fully by that time, and if schizophrenia is present, it has usually
already become apparent.