Heavy use of marijuana might increase the risk of schizophrenia in teenagers who are predisposed to the brain disorder. That is the interpretation researchers are giving to a series of studies comparing the brains of adolescent marijuana users, schizophrenic teenagers, and healthy teens who don't use the drug.
Scientists at Albert Einstein College of Medicine in New York City found disturbing similarities in the brains of the schizophrenics and the teenaged marijuana smokers.
Using a sophisticated imaging technology, they peered into a region of the brain associated with language and hearing and known to be still under development in late adolescence. The brain scans showed the same abnormalities in both the marijuana users and schizophrenics, but not in the healthy group of teens.
The findings were presented at the annual meeting of the Radiological Society of North America in Chicago. Albert Einstein College researcher Manzar Ashtari says they suggest that marijuana use alters a part of the brain as it develops, the same area that is damaged in the schizophrenic brain.
"Our conclusion is that smoking marijuana during adolescence interrupts brain maturation and damages the developing brain area," said Mr. Ashtari. "So adolescents who are genetically predisposed to have schizophrenia are increasing their chance of contracting the disease by smoking marijuana."
Schizophrenia affects nearly one percent of the world population. It is a group of disabling mental illnesses characterized by disturbances in thinking, emotional reaction, and behavior. It causes a wide array of symptoms, from social withdrawal to hallucinations.
The damage the brain scans found in both the schizophrenics and teenagers who smoke a lot of marijuana was to the protective fatty insulation called myelin around brain nerve fibers, or axons. The researchers saw that the axon fibers in both groups were not myelinated, or lacked myelin.
But the study results are being received with caution by physician Michael Brant-Zawadzki, the chairman of the Radiological Society of North America's communication committee, who was also at the conference in Chicago. He notes that the study was small, involving only 77 participants. Dr. Brant-Zawadzki asked Ms. Ashtari if the lack of myelin in the teen marijuana users is really related to the toxic substances from the smoke.
"The region you are measuring is known to be the region in the brain that normally myelinates last," said Dr. Brant-Zawadzki. "In other words, the cabling gets its insulation last in terms of time of development of the brain. How do we know that you're not simply measuring delayed myelination in marijuana smokers, because they are less physically active and therefore don't stimulate myelin deposition around those axons?"
Dr. Brant-Zawadzki says the research does not show if the delay in myelin formation in the brains of adolescent marijuana smokers is permanent. Dr. Ashtari and her colleagues say larger, longer-term studies are needed to answer this question.