Nearly half of these men “take pain medication of a daily basis, and in nearly two-thirds of these cases they take prescription pain medication,” Krueger wrote. “Labor force participation has fallen more in areas where relatively more opioid pain medication is prescribed.”

Asked whether painkillers are the reason they aren’t working — or whether these men turn to painkillers as a result of prolonged unemployment — Krueger had an answer at the ready.

“It is very likely some of both,” Krueger wrote Friday in an email to NBC News.