More than one in five people prescribed extended-release painkillers such as OxyContin developed an addiction within a year, according to a newly released study mandated by the U.S. Food and Drug Administration.

The study, repeatedly delayed by more than a decade and released Monday, revealed a far higher percentage of pain patients addicted to opioids than drugmakers’ sales reps claimed in their marketing materials and representations to physicians.

The FDA now faces the question of how to use this data to evaluate whether the agency should make changes to opioid regulation, limiting broad approvals of long-acting opioids for extended use. The FDA is currently holding hearings to discuss the findings and is being asked by advocates to change the drugs’ labels, which guide how doctors prescribe them.

When the opioid market was thrown open to millions of chronic pain patients in the 1990s and early 2000s, Purdue Pharma’s sales reps and promotional videos asserted that fewer than 1% of patients became addicted to painkillers. Extended-release pills were designed to continually dose opioids to stave off chronic pain.

Data released Monday show that 22.5% of pain patients who started on extended-release, long-acting drugs developed opioid use disorder, or addiction, within a year. The findings stem from a post-marketing study requirement mandated by the FDA in 2013, which was funded by a consortium of opioid manufacturers including Purdue, Mallinckrodt Pharmaceuticals and Endo Pharmaceuticals – all of which have filed for bankruptcy following settlements.

“The findings are striking and disturbing and they raise ethical questions because so many study subjects were harmed,” said Andrew Kolodny, president of Physicians for Responsible Opioid Prescribing. “How can you have a label that suggests this is safe and effective when you now have evidence that it’s unsafe and still don’t have evidence that it’s effective?”

In March, Purdue filed a $7.4 billion bankruptcy plan to resolve thousands of lawsuits related to the company’s role in the opioid epidemic. A representatives for Purdue declined to comment. Spokespeople for Mallinckrodt and Endo weren’t immediately available.

Efforts to get a clear picture of exactly how addictive these long-acting opioids are have been thwarted through the years as drugmakers and patient advocates lobbied for easy access to opioids and disputed the definition of “addiction.” The epidemic has claimed more than 800,000 lives in the US since 1999 and remains a major public health problem.

Millions of Americans have become dependent on opioid pills, even as mounting evidence suggests these drugs should never have been approved as safe and effective for chronic pain. The agency’s own labeling — meant to define a drug’s use, flag its risks, and limit its marketing — helped legitimize widespread, high-dose, long-term prescribing without the clinical evidence to support it, as revealed in a Businessweek investigation.

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