WASHINGTON — Newly unearthed documents show that the Food and Drug Administration failed to use its policing powers to make sure a program to curb improper prescribing of opioids was effective, researchers say.

The lax oversight, they point out, occurred as the epidemic was growing and tens of thousands of people were dying from overdoses each year.

In 2011, the F.D.A. began asking the makers of OxyContin and other addictive long-acting opioids to pay for safety training for more than half the physicians prescribing the drugs, and to track the effectiveness of the training and other measures in reducing addiction, overdoses and deaths.

But the F.D.A. was never able to determine whether the program worked, researchers at the Johns Hopkins Bloomberg School of Public Health found in a new review, because the manufacturers did not gather the right kind of data. Although the agency’s approval of OxyContin in 1995 has long come under fire, its efforts to ensure the safe use of opioids since then have not been scrutinized nearly as much.