Researchers say that teenagers who regularly smoke marijuana risk damaging a key brain pathway associated with language development and some predisposed to schizophrenia may contract the illness early.
Apparently brain scans have revealed microscopic abnormalities in a region of the brain that governs higher aspects of language and listening functions in adolescents who are heavy marijuana smokers.
The researchers at the Albert Einstein College of Medicine in New York, scanned the brains of 114 subjects, 26 of whom were selected because they were diagnosed schizophrenics, and of the schizophrenic group, 15 smoked marijuana.
Another 15 subjects were nonschizophrenic adolescent male marijuana smokers who were matched against nonsmokers.
It was those smokers whose scans showed abnormalities in the language and listening pathway.
They say they found similar damage to the bundle of fibers, called the arcuate fasciculus, that connect the Broca's area in the left frontal lobe and the Wernicke's area in the left temporal lobe, in the brains of the marijuana smokers and the schizophrenics studied.
Psychiatry professor Sanjiv Kumra says the 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.
The researchers say that the brain's language pathway continues to develop during adolescence and is susceptible to neurotoxins introduced through marijuana use.
A scanning technique called diffusion tensor imaging, that detects and measures the motion of water molecules in the brain, was used in the study; it is not used to diagnose schizophrenia.
According to the National Institute on Drug Abuse, as many as 3 million Americans aged 12 and older use marijuana on a daily or almost daily basis.
The researchers say longer-term studies are needed to determine if the brain abnormalities observed in adolescents were permanent or not.
The study was presented at the annual meeting of the Radiological Society of North America.