Pubdate: Fri, 03 Apr 2009
Source: Chilliwack Progress (CN BC)
Copyright: 2009 The Chilliwack Progress
Contact:  http://www.theprogress.com/
Details: http://www.mapinc.org/media/562
Author: Kim Dawson
Note: Dr. Kim Dawson is a psychologist in the Child and Youth Mental Health
program as part of the Ministry of Children and Family Development,
Government of BC.
Bookmark: http://www.mapinc.org/find?252 (Cannabis - Psychosis)

REALITY CHECK : DOES CANNABIS CAUSE PSYCHOSIS?

Psychosis is a class of mental illnesses characterized by
strongly-held irrational beliefs not consistent with reality
(delusions) and bizarre sensations of objects or people that are not
actually present (hallucinations). Leading up to a psychotic episode
is  often a period including lack of motivation, lack of emotions,
and difficulty thinking or speaking in a way that makes sense to
others or oneself.

As a drug in the class of psychedelic substances, cannabis can,
within minutes after inhaling its vapors, induce psychosis-like
symptoms including hallucinations, paranoid delusions, lack of
motivation, and difficulty thinking or speaking logically. So, can
cannabis cause psychosis?

According to the BC Schizophrenia Society, the answer to the question
of whether cannabis causes psychosis is yes. This is based on many
research studies from around the world which have found that the
rates of cannabis use are about twice as high among people with
schizophrenia as among the general population. In addition, surveys
of patients with psychotic illnesses have found that 20 to 40 per
cent report lifetime cannabis use. But these elevated rates of
association between cannabis use and psychotic illness do not
resolve the question of whether cannabis use is a consequence or a
cause of psychosis.

A very large Swedish study (which had over 45,000 subjects) showed
that even when other illnesses that overlap with psychosis were
controlled for, self-reported heavy cannabis users (those who used
more than 50 times) were two times more likely than  non-users to
have been diagnosed with schizophrenia 15 years later. In a large
Netherlands study (having over 4,000 subjects), individuals with
psychotic symptoms who used cannabis were nearly three times more
likely than non-users to manifest psychotic symptoms between one and
three years later. In these studies, the association between cannabis
and schizophrenia held even after adjusting for the use of other drugs.

If you read the fact sheet available on the BC Schizophrenia
Society's website  (
www.bcss.org/2006/01/resources/family-friends/cannabis-and-psychosis),
 you will find that recent research is mounting that when someone
uses marijuana in their teens, uses heavily, and is vulnerable to
psychosis, marijuana can trigger early onset of psychotic illnesses.
Moreover, of persons with psychotic illness who don't respond to
treatment, 70 per cent or more are using cannabis or other drugs
(including nicotine, alcohol, and heroin).

But who are these vulnerable people? How does a person become
vulnerable to psychosis? A person who is vulnerable to psychosis
shows symptoms of psychosis. This might sound like circular logic.
But it is important to realize that psychosis isn't a single mental
disorder, it's a spectrum. This spectrum ranges from a brief
psychotic episode lasting for a few minutes (which can be induced by
cannabis and some other drugs), all the way to full-blown
schizophrenia which can last for years.

The findings that heavy marijuana use (50 times a year or more) can
predispose groups of vulnerable individuals to schizophrenia years
later are worth a closer look. Clearly, not all adults with
schizophrenia used cannabis in adolescence and this does put to rest
the idea that cannabis causes schizophrenia. In addition, the
majority of teenaged cannabis users don't go on to develop
schizophrenia in adulthood, so we can't conclude that cannabis use is
the only cause. But, in combination with other factors, cannabis may
have a significant influence on later development of schizophrenia,
especially if there were already psychotic symptoms when cannabis use
began.

In conclusion, it is important to realize that we cannot eliminate
cannabis use totally from the population, nor would we want to.
Marijuana has legitimate uses as a medication for pain management in
multiple sclerosis, arthritis, and other illnesses (see Health
Canada's website at   www.hc-sc.gc.ca/dhp-mps/marihuana/index-eng.php
).

Instead, it may be advisable to screen young people for symptoms of
psychosis and then focus on reducing cannabis use in vulnerable
youth. To engage youth who commonly use drugs, this would mean
designing educational approaches that are informative rather using
scare tactics. One recommended approach would be to engage young
people in an open-minded and balanced discussion of both psychotic
symptoms and drug use.

Dr. Kim Dawson is a psychologist in the Child and Youth Mental Health
program as part of the Ministry of Children and Family Development,
Government of BC.
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MAP posted-by: Larry Seguin