|
Nov. 22, 2002 — Three cohort studies
published in the Nov. 23 issue of the British Medical Journal
suggest that frequent cannabis use increases the risk of
developing depression and schizophrenia in later life.
"Given recent increasing levels of
cannabis use, measures to reduce frequent and heavy recreational use
seem warranted," write George C. Patton, from Murdoch Children's
Research Institute in Victoria, Australia, and colleagues.
This study suggests that
girls who
use cannabis as teenagers are more likely to develop anxiety or
depressive disorders. Among 1,601 students from 44 secondary
schools, frequent cannabis use predicted later depression and anxiety,
especially in girls. By age 20, 60% of participants had used cannabis,
and 7% used it daily. After adjustments for use of other substances,
daily cannabis use in young women was associated with a more than
fivefold increase in risk of later depression and anxiety (odds ratio
[OR], 5.6; 95% confidence interval [CI], 2.6-12). Weekly or more
frequent use as a teenager doubled later risk (OR, 1.9; 95% CI,
1.1-3.5).
A 1969-1970 survey of 50,087
male
Swedish conscripts, aged 18 to 20 years, showed that use of cannabis
increased the risk of schizophrenia by 30% (adjusted OR for
linear trend, 1.3; 95% CI, 1-1.5; P<.015). This study also
suggests a dose relationship with the development of schizophrenia,
because the adjusted OR for using cannabis more than 50 times was 6.7
(95% CI, 2.1-21.7).
"Cannabis use is associated
with an increased risk of developing schizophrenia, consistent with a
causal relation," write Stanley Zammit,
from the University of Wales College of Medicine in Cardiff, the UK, and
colleagues. "This association is not explained by use of other
psychoactive drugs or personality traits relating to social
integration."
Although the authors suggest that the
preponderance of evidence is that occasional cannabis use has few
harmful effects overall, repeated use is a potentially serious
risk to mental health, especially in the presence of other risk
factors for schizophrenia. These risks should be recognized in light of
current trends to liberalize or even legalize cannabis use.
The third study showed that
using
cannabis in adolescence increased the likelihood of experiencing
symptoms of schizophrenia in adulthood. Those who used cannabis
by age 15 years were at greatest risk.
"Our findings suggest that cannabis use
among psychologically vulnerable adolescents should be strongly
discouraged by parents, teachers, and health practitioners," write
Louise Arseneault, from King's College in London, U.K., and colleagues.
"Policy makers and law makers should concentrate on delaying onset of
cannabis use."
In an accompanying editorial, Joseph M.
Rey and Christopher C. Tennant, from the University of Sydney in New
South Wales, Australia, agreed with the findings and the need to limit
the use of cannabis, based on the dose-response relationship for both
schizophrenia and depression. Refraining from cannabis use could have
halved the incidence of psychosis requiring treatment in an earlier
Dutch cohort, and in the Swedish cohort, cannabis use increased the risk
of schizophrenia by 30%.
"This large effect is surprising and not
yet reflected in an increased incidence of schizophrenia in the
population," the authors write. "If true, the use of cannabis will
contribute to more episodes or new cases of the illness — food for
thought for both clinicians and legislators."
BMJ.
2002;325:1183-1184, 1195-1198, 1199-1201, 1212-1213
Reviewed by Gary D.
Vogin, MD |
