Among individuals who appear to be “mentally well,” heavy use of marijuana may predispose them to develop schizoprehenia and other “psychoses,” new research suggests.

Among 92 patients, ages 18 to 65 years, who suffered a first episode of functional psychotic illness, more than half said they smoked marijuana daily or nearly every day and most of these individuals (66 percent) had no pre-existing signs of abnormal neurological development that would put them at risk for psychosis.

They had no family history of psychosis; they had been doing well academically; they had a group of friends and as such were not socially isolated; and they had good muscle coordination, Dr. Miguel Ruiz-Veguilla, of the Institute of Neurosciences of the University of Granada, Spain, and co-investigators explain in the latest issue of the journal Schizophrenia Research.

The remaining 43 percent of the study subjects with a first psychotic episode did have signs of abnormal neurological development that increased their risk of psychosis, such as a family history of psychosis and trouble in the social and academic worlds.

The new and most interesting study finding, wrote the researchers, is that mentally healthy adults who smoke marijuana daily or nearly every day may experience psychotic symptoms, while not having any of the risk factors for these symptoms.

This study, Veguilla further explained in comments to Reuters Health, suggests that patients with poor social and academic adjustment before the onset of illness “do not need an environmental factor in order to develop psychosis.”

While people with good social and academic adjustment before the onset of psychosis illness - defined as have more than five friends; good academic function; good motor coordination and sensory integration; and no family history of psychosis - need a strong environmental factor, such as smoking cannabis every day, to develop psychosis.”

SOURCE: Schizophrenia Research 2009.