The Princeton economist Alan Krueger started with a question: What’s keeping young people out of work?

Over the last two decades, the share of employed Americans in their prime has steadily tumbled - even as the economy recovered and businesses nationwide struggled to fill openings.

In a new paper, Krueger argues that opioids pose more than just a health threat: They’re benching workers across the country.

“The problem of the depressed labor force has run into the problem of the opioid crisis,” he said. “Now they’re connected.”

The rise in painkiller prescriptions between 1999 and 2015 drove about 20 percent of the drop in men’s workforce participation and 25 percent of women’s, Krueger estimated in the study, out Thursday.

To reach this conclusion, the economist looked at county-level opioid prescription rates and labor force data from the periods of 1999 to 2001 and 2014 to 2016.

Areas with the highest rates of opioid prescriptions, Krueger noticed, also experienced a shrinking workforce. The swaths of Nevada, Michigan, Maine, the southeast and the southwest appear to have suffered the hardest hits.

He also found that unemployed men and women both reported higher use of painkillers than their counterparts with jobs.

In surveys, Krueger saw that 44 percent of out-of-work men said they’d taken pain medication within the last 24 hours, though that could include something as innocuous as ibuprofen. Still, their rate was more than double that of the working men.

Among prime age women, though, the gap was less dramatic. Some 34.7 percent of women who had dropped out of the labor force said they were taking painkillers.