A new paper released by Harvard Medical School has shown that the link between marijuana use and presence of the mental illness is negligible, as part of a comparison between families with and without a history of schizophrenia. 

“The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself,” the research team noted.

The novel study is the first one that, as the researchers said, “examines both non-psychotic cannabis users and non-cannabis user controls as two additional independent samples, enabling the examination of whether the risk for schizophrenia is increased in family members of cannabis users who develop schizophrenia compared with cannabis users who do not and also whether that morbid risk is similar or different from that in family members of schizophrenia patients who never used cannabis.”

The research team, led by Harvard’s Ashley C. Proal, shed more light on its findings, noting that “while cannabis may have an effect on the age of onset of schizophrenia it is unlikely to be the cause of illness.” “In general, we found a tendency for depression and bipolar disorder to be increased in the relatives of cannabis users in both the patient and control samples. This might suggest that cannabis users are more prone to affective disorders than their non-using samples or vice versa.” The findings give new foundations to future research conducted in the field.