Between 2002 and 2018, the number of adults aged 18-22 in the U.S. who abstained from alcohol increased from 20% to 28% for those in college and from about 24% to 30% for those not in school, say researchers at the University of Michigan and Texas State University. And alcohol abuse among both groups decreased by roughly half.

However, the study found that the number of young adults using marijuana, as well as co-using alcohol and marijuana, has increased.

Overall, the mixed findings show more positive than negative trends for alcohol and marijuana use and misuse among this age group, but the progression still bears close monitoring, the researchers say.

The study, appearing in JAMA Pediatrics Oct. 12, examined how alcohol and marijuana abstinence, co-use and use disorders have changed in 18-to-22-year-olds as a function of college status, using data from a nationally representative survey of 182,722 young adults. It also looked at prescription drug use and misuse as a function of alcohol and marijuana use, from 2015 to 2018.

The researchers were particularly surprised at the drop in alcohol use and misuse.

"We're encouraged by the significant decreases in alcohol use disorder -- for both college and noncollege students," said lead author Sean Esteban McCabe, director of the Center for the Study of Drugs, Alcohol, Smoking and Health at the U-M School of Nursing.

"The prevalence of alcohol use disorder in both groups in 2018 was roughly half of what it was in 2002. We are excited to learn about these drops in disordered drinking, as alcohol-related consequences are one of the leading causes of mortality and morbidity for young adults."

Co-author Ty Schepis, professor of psychology at Texas State, said "even with increases in marijuana use disorder and co-use of alcohol and marijuana, there is a lot of hope in our study's results."

"Points of concern that deserve more attention are the rise in co-use of alcohol and marijuana, as we know that polysubstance use can have more negative consequences and be more difficult to treat," he said.

The study also found that more than three-fourths of those who had disordered use of both alcohol and marijuana reported past-year prescription drug use and illicit drug use, while the majority reported prescription drug misuse.

The findings indicate that the substance use landscape has changed over the past 20 years, with more young adults using or misusing several different substances, as opposed to just marijuana or alcohol.

"For example, from 2015 to 2018, only 2.5% of young adults who abstained from both alcohol and marijuana reported misusing prescription drugs, while 25.1% of co-users misused prescription drugs," Schepis said. "That is a tenfold difference with potentially dangerous consequences."

Abusing multiple substances is often more dangerous than abusing a single substance.

"Interventions that focus solely on one substance will be less effective than interventions that take a more holistic polysubstance use perspective," McCabe said. "The findings of our study reinforce the complex task health professionals have of detecting and developing effective interventions to reduce consequences associated with polysubstance use, such as co-use of alcohol and marijuana."

Schools and employers may require more resources to scale interventions to address both young adults with and without a disorder, including screening and brief interventions for co-use of alcohol and marijuana, McCabe said.

"The finding that abstinence is increasing among college students and young adults not in college is very important for U.S. colleges and universities to take into account moving forward," he said. "These findings reinforce the importance of the need to support those young adults in recovery and abstinence for other reasons. There are over 1 million U.S. young adults in recovery and a wide variety of resources are needed to support these individuals."

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Materials provided by University of Michigan. Note: Content may be edited for style and length.

Journal Reference:

1. sean Esteban Mccabe, Brooke J. Arterberry, Kara Dickinson, Rebecca J. Evans-Polce, Jason A. Ford, Jennie E. Ryan, Ty S. Schepis. Assessment of Changes in Alcohol and Marijuana Abstinence, Co-Use, and Use Disorders Among US Young Adults From 2002 to 2018. JAMA Pediatr., 2020 DOI: 10.1001/jamapediatrics.2020.3352