Cannabis and schizophrenia
Schizophrenia is a mental illness characterised mainly by hallucinations and delusions (psychosis) which for the majority of people has an onset in late adolescence or early adulthood. Many people across many cultures, especially the young, use cannabis, a plant containing the psychoactive component delta-9-tetrahydrocannabinol.
More on our website about schizophrenia, including symptoms, causes and treatment
This plant, which is usually smoked or eaten, gives a feeling of well-being, but in high doses it may also cause psychosis and those who have schizophrenia may have a worse overall outcome from using it. There are some people with schizophrenia however, who claim that using cannabis helps their symptoms and reduces the adverse effects of antipsychotic medication. This review aims to look at the effects of cannabis, both its use and withdrawal, in people who have schizophrenia.
Four relevant studies were identified but three of these are awaiting assessment because further information is being sought from the trial authors. The last trial was based in a youth mental health service centre in Australia. It looked at whether a specific intervention using education on cannabis and psychosis and trying to motivate change (Cannabis and Psychosis Therapy CAP) or a series of general lectures explaining psychosis, treatments and relapse prevention (psychoeducation PE) was more likely to reduce the use of cannabis. The trial contained 47 people, 23 in the CAP group and 24 in the PE group. There were no significant differences between these two groups in the mental state of the people concerned after three months and nine months. There was also no significant difference in the use of cannabis, and knowledge on mental health and cannabis was the same in both groups.
The main problem with this trial was the small number of people studied, and perhaps differences between the treatments would emerge with a larger number of people taking part. Overall, at present, it is still not possible to say whether using cannabis causes an improvement or a deterioration of the mental health of people with schizophrenia.
