MILWAUKEE — When faced with intense criticism for her agency’s approval of the powerful narcotic painkiller Zohydro, U.S. Food and Drug Administration Commissioner Margaret Hamburg turned to a sobering statistic: 100 million Americans are suffering from severe chronic pain, she said.

The 100 million figure has become a central part of the debate over the use of narcotic painkillers.

It is cited in news stories, by medical organizations and by drug companies seeking approval for new opioid therapies. When Hamburg spoke in April at a prescription drug conference, she noted it means debilitating pain affects more people than heart disease, cancer and diabetes combined.

That number — the equivalent of more than 40 percent of the U.S. adult population — is exaggerated and misleading, according to pain experts familiar with how it was derived.

It came out of a report ordered by Congress that was introduced by lawmakers who have received hundreds of thousands of dollars from drug manufacturers. Companies that make pain treatment lobbied for the bill. The measure also was backed by pain organizations that get opioid industry funding and, in turn, had several of their members serve on the panel.

Legislation authorizing the report was rolled into the Patient Protection and Affordable Care Act — better known as the Obamacare reforms. It required the federal government to enter into an agreement with the Institute of Medicine “to increase the recognition of pain as a significant public health problem in the United States.”

A Milwaukee Journal Sentinel/MedPage Today investigation found that nine of the 19 experts on the panel that produced the number had financial connections to companies that manufacture narcotic painkillers within three years of their work on the report.

In February, two experts connected with the pain report said the 100 million figure was exaggerated and misleading and they raised concerns about how it was being used. Their comments came at a meeting of pain experts held at the National Institutes of Health.

In a video of the meeting, Allan Basbaum, one of the reviewers of the Institute of Medicine report, said he was stunned when he saw the 100 million figure.

“If we are concerned about the message we are sending, we shouldn’t exaggerate the message because the eyeballs start to roll,” said Basbaum, a professor of anatomy at the University of California, San Francisco. “The message will be more powerful if people can believe it.”