The data come from the National Survey on Drug Use and Health, an annual survey of 12- to 17-year-olds from all 50 states that is sponsored by the Substance Abuse and Mental Health Administration, an agency of the U.S. Department of Health and Human Services. The data include information from 2003 through 2014, the last year for which survey numbers are available. A total of 210,599 teens — 13,000 to 18,500 each year — were part of the study.

The findings are reported Oct. 25 in the journal Psychological Medicine.

The researchers found that the number of substance-use disorders among 12- to 17-year olds had declined by 49 percent over the 12-year span, along with a simultaneous 34 percent decline in delinquent behaviors, such as fighting, assault, stealing, selling drugs or carrying a handgun.

The drop in substance abuse among teens parallels findings in other recent surveys, but until now no one has looked at how the drop-off may be linked to other behavioral issues.

“We’ve known that teens overall are becoming less likely to engage in risky behaviors, and that’s good news,” said first author Richard A. Grucza, PhD, a professor of psychiatry. “But what we learned in this study is that the declines in substance abuse are connected to declines in delinquency. This suggests the changes have been driven more by changes in adolescents themselves more than by policies to reduce substance abuse or delinquent behavior.”

Other researchers have found that teens are delaying sex and using seat belts more often than their parents and grandparents. Grucza’s team focused on substance-use disorders — involving alcohol, nicotine, marijuana, opioids and the abuse of other prescription drugs or nonprescription drugs — and delinquent behaviors.

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