Skip to Main Content

Study shows marijuana use interrupts adolescent brain development

Kuei Y. Tseng was awarded $1.95 million by NIH for a five-year study of "Adolescent Maturation of the Prefrontal Cortex: Modulation by Cannabinoids."

Regular marijuana use by teens can stop the brain from maturing, according to a new study by scientists at Rosalind Franklin University of Medicine and Science, North Chicago, IL.

Published March 4 in the journal Molecular Psychiatry, the study is the first to establish a causal link between repeated cannabinoid exposure during adolescence and an interruption of the normal maturation processes in the prefrontal cortex, a region in the brain's frontal lobe, which regulates decision ­making and working memory and undergoes critical development during adolescence.

The findings apply to natural cannabinoids, including those in marijuana, and a new generation of more potent, synthetic cannabinoid products. THC, the compound in marijuana that produces feelings of euphoria, is of particular concern. The chemical can be manipulated, resulting in varying concentrations between marijuana strains – from 2 to 28 percent. A higher concentration of THC and increasing use by younger teens poses a greater risk for long­term negative effects, the study finds.

Kuei Y. Tseng, MD, PhD, associate professor of cellular and molecular pharmacology at the Chicago Medical School at RFUMS and principal investigator of the study, blames the CB1 cannabinoid receptor, which governs neuronal communication, for the drug's long ­lasting effect.

Tseng and his team of researchers used rat models in testing the effect of cannabinoid exposure during narrow age windows and analyzed the way information is later processed by the adult prefrontal cortex. They discovered that when CB1 receptors are repeatedly activated by cannabinoids during early adolescence, development of the prefrontal cortex stalls in that phase. The window of vulnerability represents two­ thirds of the span of adolescence. Test animals showed no such effect when exposure occurred in late adolescence or adulthood.

"We have conclusively demonstrated that an over activation of the CB1 receptor during the window equivalent to age 11 to 17 in humans, when the prefrontal cortex is still developing, will inhibit its maturation and have a long ­lasting effect on its functions," Tseng said.

The study shows how chronic cannabis use by teens can cause persistent behavioral deficits in adulthood, including problems with attention span and impulse control. The findings also add to prior research that draws a correlation between adolescent marijuana abuse and the development of schizophrenia.

The discovery, which comes as a growing number of states are considering legalization of marijuana for both medicinal and recreational use, calls for the attention of physicians who prescribe medical marijuana and policy makers who, according to Tseng, "will have to establish regulations to take advantage of the beneficial effects of marijuana while minimizing its detrimental potential."

Researchers are focusing on developing outcome measures to reveal the degree of frontal lobe maturation and history of drug exposure. The challenge now, Tseng said, is to find ways to return the frontal lobe back to a normal state either through pharmacological or cognitive interventions.

"Future research will tell us what other mechanisms can be triggered to avoid this type of impairment of the frontal lobe," Tseng said. "Ultimately, we want to restore the prefrontal cortex."

Supported by RFUMS, the research was funded primarily through NIH Grant R01­MH086507 to Tseng and also by a 2012 seed grant from the Brain Research Foundation.