Chronic use of alcohol and marijuana by teens can lead to impaired brain function later in life. That’s the conclusion of a new study that found diminished neural structure, brain size and cognitive abilities in young people who abused the drugs.
“Research has shown differences in the brains of teens who use alcohol and marijuana as compared to teens who do not use these drugs or report only very infrequent, minimal use,” said lead author Joanna Jacobus, a postdoctoral fellow at the University of California, San Diego.
“Alcohol and marijuana may have a negative impact by altering important cellular communication in the brain, preventing development of new healthy cells, which can adversely impact healthy brain development in many ways.”
Researchers followed 92 adolescents, ages 16 to 20, for 18 months. They were divided into two groups; those with extensive alcohol and marijuana use and those with little, if any, substance use.
Both groups underwent diffusion tensor imaging and detailed substance use assessments, along with toxicology screenings and interviews every six months.
“We found evidence for poorer white matter tissue health in teens who engage in heavy alcohol and marijuana use compared to those who abstain,” said Jacobus.
Describing white matter as the “information highway of the brain,” Jacobus noted that damaged white matter can mean slower cognitive processing and poorer cognitive performance such as memory, attention, and decision-making. Previous studies had not shown a clear association between alcohol and marijuana use and white matter disorganization.
“White matter organization was particularly compromised in an area (of the brain) called the superior longitudinal fasciculus,” added Duncan Clark, a study co-author and an associate professor of psychiatry at the University of Pittsburgh Medical Center. “When the connections between brain areas are severely damaged, those areas of the brain cannot properly function.”
Researchers say neural systems in teenage brains are not yet fully matured and brain connections important for inhibiting risky behaviors are still forming.
“Our findings underscore that early initiation of alcohol and marijuana use can have negative implications on the brain” said Jacobus. “We hope this information can be communicated to teens to help them understand why drinking during adolescence is discouraged.”
The study was published in a special online issue of Alcoholism: Clinical & Experimental Research, the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism.