Oct. 12 (UPI) -- Nearly one-third of all college students in the United States smoke marijuana, a study published Monday by JAMA Pediatrics found.
Roughly twice as many -- 62% -- drink alcohol, the data showed.
At the same time, the number of students who say they abstain from both has increased to 28% from just under 20% in the early 2000s.
The percentage of college students who meet the criteria for alcohol use disorder also has declined to 10% over the same period from just under 20%, they said.
"Abstinence from both alcohol and marijuana have increased," study co-author Ty Schepis,, professor of psychology at Texas State University, told UPI.
And "the number of young adults with alcohol use disorders has significantly declined, [and] the same is true with combined alcohol and marijuana use disorders," he said.
The findings are based on an analysis of data from the National Survey on Drug Use and Health for the period of 2002 through 2018, which included information on alcohol and marijuana consumption for between 7,000 and 11,000 young adults annually.
In 2018, 31% of college students reported using marijuana, up from 27% in 2002, the data showed.
However, the percentage of students who met the criteria for marijuana use disorder remained stable over the study period, at about 6%, the researchers said.
Marijuana use disorder is a "problematic pattern of ... use leading to clinically significant impairment or distress," according to the Diagnostic and Statistical Manual of Mental Disorders.
Although 62% of college students drank alcohol in 2018, a slight increase from 60% in 2002, the number who met the criteria for alcohol use disorder dropped by half over the same period, the data showed.
People with alcohol use disorder find that "drinking -- or being sick from drinking -- often interfere[s] with taking care of [their] home or family" and causes problems at work, school or home, according to the Diagnostic and Statistical Manual of Mental Disorders.
Still, the percentage of students who reported co-use of alcohol and marijuana increased to 24% in 2018 from 17% in 2002. Young adults who were not in college reported roughly the same rates of alcohol and marijuana use, the researchers said.
"It is helpful for parents to know about the changes in the substance use landscape among adolescents and young adults," study co-author Sean Esteban McCabe told UPI. "These findings remind us that we need comprehensive plans for the full continuum of relationships people have with substances," he said.
"Parents can play a key role by having candid conversations with their kids about how they fit into the substance use landscape and discuss how their strategies are working during challenging times," said McCabe, director of the University of Michigan's Center for the Study of Drugs, Alcohol, Smoking and Health.