Few substance abuse programs in the U.S. offer high-quality treatment designed specifically for adolescents, a new study finds.

Of the more than 700 treatment programs the study surveyed, less than one-third had specialized services for teenagers — with some excluding underage patients altogether and others integrating them with adult patients.

And among programs that did offer adolescent-only services, the quality was typically middling, according to findings published in the Journal of Substance Abuse Treatment.

The results may help explain why most teenagers who need substance abuse treatment do not get it, said researcher Dr. Hannah Knudsen, of the University of Kentucky in Lexington.

"We have known that out of 1.4 million teens needing help for substance abuse, one tenth of those get treatment," Knudsen said in a news release. "Part of this treatment gap may be driven by the limited availability of adolescent-only treatment services."

To gauge the quality of adolescent-only programs, Knudsen interviewed managers at 154 centers. She found that on average, the programs offered half of the components considered to be markers of high- quality, comprehensive care.

Few programs, according to the researcher, scored high in all quality "domains" — such as whether the program involved families in the treatment, or offered comprehensive services such as treatment of depression and other mental health disorders.

"The lack of comprehensive services in substance abuse programs for teens raises questions about whether teens will get what they need, since we know they are likely to have co-occurring psychiatric conditions and to engage in HIV risk behaviors," Knudsen said.

The researcher did find that the 30 percent of programs that included intensive inpatient or residential treatment — and not only outpatient services — tended to rank higher in quality.

"For parents who are looking for high-quality programs that offer the most comprehensive array of services," Knudsen said, "a good proxy indicator is whether that organization has an inpatient or residential level of care."

However, they may have difficulty finding such programs, according to the researcher. The limited availability of adolescent-only services in general, she writes, "raises a significant barrier to helping adolescents who have substance use disorders."