(CNN) The US Food and Drug Administration can't show a key program meant to address opioid misuse and abuse actually paid off, according to a new study.

The authors of the study, published Monday in the journal JAMA Internal Medicine, reviewed more than 9,700 pages of FDA documents pertaining to the agency's "risk evaluation and mitigation strategy," which launched in 2012 to address risks associated with extended-release and long-acting opioids.

Although these drugs "can be clinically useful among appropriately selected patients, they have also been widely oversupplied, are commonly used nonmedically, and account for a disproportionate number of fatal overdoses," the authors write.

As part of the FDA's strategy to clamp down on inappropriate prescribing and misuse of these drugs, the agency mandated that drugmakers offer education on safe prescribing, and that they create medication guides informing patients of risks. The FDA also required companies to provide reports on prescriber behavior and patient safety.

But the new study concluded that "more than 5 years after implementation, the FDA was unable to assess whether these outcomes were achieved."