A growing number of U.S. adults are misusing benzodiazepines such as Valium and Xanax, researchers at the University of Michigan have found.

In a study published in Psychiatric Services, the researchers report about one in five people who take benzodiazepines are misusing them.

Young adults ages 18 to 25 are the most likely to misuse benzodiazepines, the study found. “If you look at younger adults, basically misuse was as common as prescribed use, which obviously is kind of disturbing,” lead researcher Donovan Maust told HealthDay. Misuse of the drugs declined with age.

Overall use of the drugs among adults is more than twice as high as previously reported, with almost 13 percent of adults using benzodiazepines within the past year.