Opioid use is declining among high school seniors, a new study suggests.

The study, published in the journal Pediatrics, looked at prescription opioid use nationwide among high school seniors from 1976 to 2015. Teens were asked whether a doctor had ever prescribed them opioids, and how often they had taken prescription opioids without a doctor’s instruction.

About one-fourth of seniors said they had used opioids at least once for any reason, NPR reports. The study found opioid use in this age group rose in the 1980s, decreased in the 1990s and increased in the early 2000s, before dropping again starting in 2013.

“It is our hope that these declines are due to careful prescribing practices and enhanced monitoring of prescription opioids among adolescents that will eventually translate to a reduction in negative opioid-related consequences, such as overdoses,” said lead author Sean Esteban McCabe of the University of Michigan Substance Abuse Research Center.