While many still debate the potential for marijuana to cause schizophrenia, researchers at Harvard Medical School say there has "yet to be conclusive evidence that cannabis use may cause psychosis."

Their latest study, published in the journal Schizophrenia Research, adds support to the role of genetic factors in schizophrenia, and that marijuana use alone does not increase the risk of developing the disorder.

"In summary, we conclude that cannabis does not cause psychosis by itself. In genetically vulnerable individuals, while cannabis may modify the illness onset, severity and outcome, there is no evidence from this study that it can cause the psychosis."

The team, led by Lynn DeLisi, MD, Professor of Psychiatry at Harvard Medical School, compared the family histories of 108 schizophrenia patients and 171 individuals without schizophrenia to determine whether cannabis use was a factor in developing the disorder.

They found that a family history of schizophrenia increased the risk of developing schizophrenia, regardless of whether or not an individual used cannabis.

The authors say further studies should investigate whether marijuana can interact with genetic factors to affect the age at which schizophrenia develops. However, the latest findings provide enough evidence for Dr. DeLisi and her team to conclude that cannabis "is unlikely to be the cause of illness."

Interestingly, the authors also point out that different types of marijuana may play a role in the outcome of schizophrenia.

"The amount of THC is particularly of concern, whereas CBD is the component that is thought to have medicinal value even in schizophrenia."

Indeed, although THC is known to have psychosis-like effects, there is growing evidence that CBD can counter the effects of THC, and may even be useful as a treatment for schizophrenia.

The study received funding from the National Institute on Drug Abuse (NIDA)

Source: LeafScience