Use of marijuana during adolescence significantly increases the risk of schizophrenia among young people with a genetic predisposition to the disease, according to a new study by Israeli and American researchers.
The study was recently published in the journal Human Molecular Genetics.
During the research, which was done on mice, the scientists identified the biological mechanism that contributes to the outbreak of the illness while using marijuana, hashish and a synthetic drug known as “Nice Guy.” The study was conducted by researchers at Tel Aviv University, Geha Psychiatric Hospital and Johns Hopkins University in Baltimore.
Schizophrenia, a chronic mental illness, affects nearly 1 percent of the population, meaning some 80,000 Israelis suffer from it. The neurological reasons for the development of the disease are still not clear, and studies from recent years have shown that more than a hundred different genes are involved in its appearance.
“Schizophrenia is a serious disease that appears during adolescence, apparently on a background of genetics and environmental damage,” said Prof. Daniel Offen of TAU, one of the researchers.
“Unfortunately the range of genes that are liable to trigger schizophrenia is still not clear, but it’s known that a number of genes, when mutated, may raise the risk of the disease. One of those genes is called DISC-1. In the study we examined whether use of THC – the active ingredient in cannabis – could advance the onset of the disease or worsen it.”
The researchers used young mice with a defective DISC-1 gene and treated them with THC for a few days. Afterward the mice went through a number of behavioral and biochemical tests. A control group of mice whose DISC-1 gene was undamaged was given identical THC treatment.
“Among the young mice with the damaged gene that were exposed to THC, we saw a significant increase in behavioral symptoms linked to schizophrenia, including impaired brain function,” said Hadar Segal Gavish, a research student on the TAU team.
“We know from previous studies that adolescence is a critical period for the onset of the disease. In the new study we found that at a young age, the combination of genetic predisposition and use of THC worsens the symptoms.”
The researchers also found that while healthy mice could increase their production of a brain protein called BDNF to neutralize the effects of THC, in the mice with the defective gene the levels of BDNF remained the same. At another stage the researchers injected BDNF into the brain’s hippocampus (the area that creates new memories) and demonstrated that an increased presence of the protein blocked the damage caused by THC.
Claim of link not new
The claim of a link between marijuana consumption in teens and the risk of developing mental illnesses like schizophrenia is not new. Use of marijuana, cocaine and LSD are recognized risk factors for their onset. According to Dr. Ran Barzilay, one of the TAU researchers who is also a pediatric psychiatrist at Geha, the new research is consistent with clinical findings.
“As someone who works with teenagers, I see a lot of young people aged 15 to 25 who suffered outbreaks of the disease in proximity to their use of cannabis or synthetic cannabis,” he said. “Over the past two years there have been large studies, particularly in England, that showed a connection between the quantity and strength of the material and the age of use, and the onset of illnesses like schizophrenia. The stress is on adolescence, which is a particularly vulnerable window of time. Our study tried to imitate in a mouse model the clinical picture we were seeing in patients.”
Barzilay added: “There are young people with a certain genetic profile who could live peacefully until 120, but if those same young people are exposed to marijuana, hashish or ‘nice guy,’ the chances of schizophrenia presenting itself are very high.”
The impact of marijuana use on young people has been occupying scientists and law enforcement officials in Israel and elsewhere, especially since teens today are less likely to consider marijuana a risky drug. A survey of 14,000 teens in Israel in 2014 by the Anti-Drug Authority and Bar-Ilan University showed that in only three years (from 2011 to 2014), there was a more than 60 percent increase in the ratio of 10th graders who had tried marijuana, reaching a total of 8.8 percent of secular Jewish 10th graders and 11 percent of Arab 10th graders.