Heavy use of marijuana may put adolescents who are genetically predisposed to schizophrenia at greater risk for developing the disease, according to a presentation at the annual meeting of the Radiological Society of North America.

Using a sophisticated brain imaging technique called diffusion tensor imaging (DTI), American researchers studied the brains of groups of adolescents: healthy, non-drug users; heavy marijuana smokers (daily use for at least one year); and adolescents with schizophrenia.

Unlike magnetic resonance imaging (MRI), which provides a static picture of brain structures, DTI detects and measures the motion of water molecules in the brain, which can reveal microscopic abnormalities.

Manzar Ashtari, PhD, and colleagues used the technique to examine the arcuate fasciculus, a bundle of fibers connecting the Broca’s area in the left frontal lobe and the Wernicke's area in the left temporal lobe. The investigators found that repeated exposure to marijuana was related to abnormalities in development of this fiber pathway, which is associated with higher aspects of language and auditory functions.

"Because this language/auditory pathway continues to develop during adolescence, it is most susceptible to the neurotoxins introduced into the body through marijuana use," explained Ashtari, associate professor of radiology and psychiatry at New York's Albert Einstein College of Medicine.

In the current research, imaging was performed on 12 healthy, early adolescent males compared with 12 late adolescent males to show normal human brain development; 11 schizophrenic patients compared with 17 matched controls; 15 schizophrenic patients who smoked marijuana compared with 17 matched controls; and 15 marijuana smokers compared with 15 matched non-drug users.

The scans revealed no abnormal developmental changes in the language pathway in the healthy adolescents, but showed abnormalities in both the marijuana users and schizophrenic patients.

"These findings suggest that in addition to interfering with normal brain development, heavy marijuana use in adolescents may also lead to an earlier onset of schizophrenia in individuals who are genetically predisposed to the disorder," said co-principal-investigator Sanjiv Kumra, MD, assistant professor of psychiatry at Albert Einstein College of Medicine.

According to the National Institute on Drug Abuse, approximately 3.1 million Americans age 12 years and older use marijuana on a daily or almost daily basis.