Psychoactive substance use (PSU) in patients with schizophrenia can affect the course of the disease and causes many side effects. There is no clear evidence whether cannabis use can trigger the first episode of schizophrenia. The main causes of cannabis use in patients with schizophrenia are also still not defined.

Determine causes of PSU in cannabis users with schizophrenia.

The aim of this study was to find out the causes of PSU in patients with schizophrenia.

Thirty-five cannabis users with schizophrenia (28 males, 7 females) were asked to complete 15-item questionnaire about the reasons of psychoactive substance intake. Eighteen of them used also stimulants. Additional information if PSU or schizophrenia occurred first was also taken.

The results indicated that regardless of stimulants use PSU occurred before schizophrenia in 83% of patients. Main reasons of substance intake were: need for relaxation (86%) which was more often in marihuana group (100%) than in marihuana and stimulants group (73.7%) and this difference was statistically significant (P = 0.049), curiosity (80%), self-regulation of well-being (74%), shyness, need for altered states of consciousness, expectation that psychoactive substances could help them in problem solving, relationships and sleep disorders (49–54%).

PSU usually occur before the first episode of schizophrenia. Anxiety, curiosity and looking for unprofessional help are the most common reasons. The results may indicate an increased need of psychoeducation and social support in many areas of life. Future research should be considered.

The authors have not supplied their declaration of competing interest.