Abstract:
Cannabis is the most widely used illegitimate substance in the world, and the
number of users has increased by 10% over the last decade worldwide. Therefore,
it is important to review the evidence on psychoactive properties of cannabis and
its possible association with schizophrenia spectrum disorders (SSD). We searched
MEDLINE with the key words cannabis and schizophrenia. The search was limited to
articles published in English over the last 10 years (1999-2009). Bibliographies
of cited literature were also searched. Data sources included reviews published
in core clinical journals, cohort studies, interventional studies, case-control
studies, cross-sectional analyses and epidemiological data. Results are discussed
under 2 topics. Firstly, evidence related to biochemical functioning of
cannabinoids and their relationship to endocannabinoid system is discussed
briefly. Secondly, the evidence from clinical studies on cannabis, psychosis
proneness and SSD are discussed in detail. The discussion is structured to fit in
the evidence from results section to 3 plausible hypotheses on cannabis use and
SSD. The evidence for and against each hypothesis is discussed. Despite new
evidence, the exact relationship between cannabis and SSD is unclear. There is no
firm evidence that cannabis causes SSD. The evidence for the argument that
schizophrenic patients are attracted to cannabis is also not strong. The most
plausible explanation is that cannabis use and psychosis proneness may have
synergistic effects in a vulnerable minority.
