A new UT Dallas study has found that having family or friends involved in crime was the best predictor of whether a youth offender would become a long-term marijuana user or heavy drinker.

The study was the result of interdisciplinary collaboration by Dr. Alex Piquero, associate dean of graduate programs and Ashbel Smith Professor of Criminology in the School of Economic, Political and Policy Sciences; associate professor Dr. Francesca Filbey at the Center for BrainHealth in the School of Behavioral and Brain Sciences; and three co-authors from other universities.

Their work was recently published in the journal Psychology of Addictive Behaviors.

The authors studied a sample of 1,354 youths ages 14 to 17 — mostly male — who had been adjudicated or convicted of serious offenses including violent crimes, property crimes, weapons and sex crimes. Researchers evaluated a variety of factors, including demographics, family arrest histories, education, impulsiveness, intelligence, neighborhood and peers. They followed up with the participants regularly over seven years.

The researchers initially projected that the neighborhood issues — gangs, delinquent peers, unmonitored activities and gun carrying — would be the strongest contributor to long-term substance abuse. Delinquent peers and family arrests played a greater role than expected. Lack of ability to control impulses also emerged as a top factor.

The findings underscore the importance of training youths to strengthen impulse control and resist peer pressure as part of drug and alcohol abuse prevention programs, Piquero said.

“Policywise, efforts at improving self-control and increasing resistance to peer antisocial behavior appear to be critical in preventing heavy substance use,” he said.

Neuropsychological factors — IQ and other cognitive measures — did not play as big a role as the other factors.

“Existing cross-sectional studies show that substance abusers exhibit poorer cognition,” Filbey said. “What this work presents is that, although neuropsychological factors don’t appear to increase risk, decreased cognitive function is likely an effect, rather than a cause, of substance use. This would suggest that changes in the brain occur following substance use.”