Many people with the serious mental illness and schizophrenia smoke cannabis but it is not known why people do so or the effects of smoking cannabis. It is unclear what the best methods are that help people to reduce or stop smoking cannabis. Cannabis is the most consumed illicit drug in the world – amounting to 120 to 224 million users. Cannabis, which is usually smoked or eaten, gives a feeling of well-being, but in high doses it may also cause mental illness or psychosis. Clinical evidence suggests people who have schizophrenia have a worse overall outcome from using cannabis, however, there are some people with schizophrenia who claim that using cannabis helps their symptoms and reduces the side effects of antipsychotic medication. This review aims to look at the effects of cannabis, both its use and withdrawal, in people who have schizophrenia. A search for trials was conducted in 2013, eight randomised trials, involving 530 participants were included. Five trials investigated the effects of using a specific psychotherapy aimed at reducing cannabis intake, two investigated the effects of antipsychotic medication for cannabis reduction and one investigated the use of cannbidiol (a compound found in cannabis) as a treatment for the symptoms of schizophrenia.
The results of the review are limited as trial sizes were small and data were poorly reported.
Overall, there is currently no evidence for any intervention, whether it is psychological therapy or medication, being better than standard treatment or each other in reducing or stopping the use of cannabis. More research is needed to explore the benefits of medication or psychological therapy for those with schizophrenia who use cannabis. It is unclear if cannabidiol has an antipsychotic effect.
See more at: http://summaries.cochrane.org/CD004837/SCHIZ_cannabis-for-schizophrenia