Do expected effects of cannabis relate to the experiences people have
when using the drug? An individual’s expectancies for a substance capture how
they expect to be affected during substance use and are shaped by information
from the environment (e., media, peers, observing others) as well as subjective
experiences with that particular substance when use occurs . Traditionally,
expectancies have been considered in alcohol research, and are related to both
adult and adolescent drinking behaviours. More recently expectancies have been
investigated in relation to cannabis use, with the previous results from
alcohol research largely being replicated [6-8]. Given the role for
expectancies to shape patterns of substance use, the investigation of cannabis
expectancies has relevance not only for substance use problems in the general
(psychologically healthy) population, but also for individuals with serious
mental health problems. For instance, compared to the general population, rates
of cannabis use are elevated in patients with schizophrenia and psychosis prone
healthy volunteers from the general population.
In those with schizophrenia,
substance use can lead to variability in treatment and symptom outcomes.
Therefore determining whether cannabis expectancies vary according to
vulnerability for a mental illness such as schizophrenia could highlight
reasons for use, potentially explain variations in subjective experiences with
a substance and assist in the development of effective psychological
interventions to target substance use in psychologically vulnerable
populations.
Few studies have investigated cannabis expectancies in patients with
schizophrenia. Green, Kavanagh and Young reported that patients with psychosis
had the same expectancies for cannabis and used the same quantities on each
occasion but with less frequency when compared to healthy controls. However,
psychosis patients displayed more cannabis dependent-like behaviours (e.g.,
withdrawal symptoms) and were more driven to change their consumption than
healthy controls. Self-reported negative effects of cannabis predicted of
cannabis use over a four week follow up period in the patients with psychosis but
not control participants. Despite there being no differences between the
patients and controls on their overall expectancies for cannabis, cannabis
expectancies appeared to behave in differential manner in the two groups.
