Implicit and explicit expectancies of cannabis use in patients with schizophrenia

A lot of patients with schizophrenia use cannabis. Cannabis use has an adverse
impact on positive symptoms, compliance and prognosis. Patients say they use
cannabis to enhance positive mood, and to cope with negative emotions.

To improve treatment for cannabis using schizophrenia patients, it is neccesary
to get more insight in their motivation and expectancies of cannabis use. These
expectations can be measured in an explicit and implicit way.

Explicit expectations of cannabis use have been studied in the general
populations as well as in patients with schizophrenia, with contradictory
results. There are studies in which expectations between patients and controls
do not differ, on the other hand there are studies in which the self-medication
hypothesis is confermed, therfore the results point out there is an
'extra'reason for patients to use cannabis, namely to alleviate their symptoms
and side-effects of antipsychotics. Implicit expectations are expectations that
people are unaware of. Implicit expecatations are measured in alcohol and drug
research, but have never been tested in patients with schizophrenia.

This study will assess both implicit and explicit effect expectancies
associated with marijuana in individuals with psychotic disorder. We will
determine whether such expectancies are different from those of people in the
general population. We will determine whether the explicit expectancies are
associated with personal drug use patterns, craving and implicit expectancies.
Through this research we hope to develop more insight in cannabis related
cognitions in patients with psychotic disorder. Most important we hope to get
an answer to the question whether patients with psychotic disorder use cannabis
as 'self-medication', to alleviate their symptoms or side-effects of
anti-psychotic medication. A valid assessment of implicit and explicit
expectancies of cannabis use will hopefully contribute in developing more
insights in specific interventions for drug use disorder in patients with
psychotic disorder. Knowledge of cannabis related cognitions in patients who
never used cannabis, will also contribute in developing preventative measures,
which is very important, because cannabis use has an adverse impact on the
course and outcome of psychotic disorder.

It is a cross-sectional study design. Participants will be invited for one
assessement in which two short interviews will be done, two questionnaires will
be filled out and a computer task will be done. Participants are asked whether
they may be invited for follow up 6 months after baseline for a short interview
and a questionnaire they have to fill in.
Patients will be compared to healthy subjects.
It is expected that 200 participants will be included in this study.

There is no burden and risk associated with participation.
participants are seen once by a research assistant, for two short interviews,
two questionnaires an a computer task. This takes one hour all together.
Questions mainly focus on cannabis use and expectancies of cannabis use.

Participants are asked whether they can be assessed one more time after 6
months for two questionnaires on use of cannabis and craving for cannabis. This
second assessment is done by one research assistant and takes 30 minutes.

Participants are of minor age as well as major age. In light of negative
effects of cannabis use on course of schizophrenia it is of great importance to
get insight into reasons for cannabis use in this population. Especially in
young patients
much healt profit is expected of improved treatment.