A new study finds teens with severe substance use disorder often continue to have symptoms of the disorder in adulthood, UPI reports.

The study, funded by the National Institute on Drug Abuse, followed more than 5,300 people who turned 18 between 1976 and 1986 for a period of more than 30 years.

Researchers found 12% of teens had severe substance use disorder. Among this group, more than 60% had at least two symptoms of substance use disorder in adulthood. They were also more likely, as adults, to use and misuse prescription medications, and self-treat with opioids, sedatives or tranquilizers, compared to those who did not have severe substance use disorder as teens.

Most of those with long-term substance use disorder did not seek treatment, the study found.

“Teens with substance use disorder will not necessarily mature out of their disorders, and it may be harmful to tell those with severe symptoms that they will,” study author Dr. Sean Esteban McCabe of the University of Michigan said in a news release.