The opioid crisis is growing in America, and it may be the reason many men are dropping and staying out of the workforce, according to a new study.

Nearly half of the men in the U.S. who dropped out of the workforce are on opioid painkillers, Princeton University economist Alan Krueger wrote in a Brookings Institute study released this week.

“The opioid crisis and depressed labor-force participation are now intertwined in many parts of the U.S.,” Krueger wrote in the Brookings Institute study.

Krueger found that nearly half of the men surveyed “take pain medication on a daily basis, and in nearly two-thirds of these cases they take prescription pain medication.”

“Labor force participation has fallen more in areas where relatively more opioid pain medication is prescribed,” he wrote.

Krueger said the men surveyed took painkillers either as a result of being out of the workforce for a prolonged period or because they had a condition that required the use of painkillers and could not work because of the condition.

“The results of this survey underscore the role of pain in the lives on nonworking men, and the widespread use of prescription pain medication,” he wrote. “Fully 47 percent of NLF (not in labor force) prime age men responded that they took pain medication on the previous day.”

He added that nearly two-thirds of the men who took pain medication said they were taking prescription meds.

“These figures likely understate the actual proportion of men taking prescription pain medication given the stigma and legal risk associated with reporting taking narcotics,” Krueger said.

NBC News cites data from the Bureau of Labor Statistics that show the labor force participation rate, comprised of people who are working or actively looking for work, reached an all-time high of 67.3 percent in the U.S. in early 2000.

The labor force participation rate reached a 40-year low in September 2015, dipping to 62.4 percent, as the American economy grew very slowly under former President Barack Obama.

Krueger said the labor participation rate in the past decade declined faster than the decade preceding it.

“The share of non-college educated young men who did not work at all over the entire year rose from 10 percent in 1994 to more than 20 percent in 2015,” he wrote.

The decline roughly coincides with the beginning of the opioid epidemic, when the number of unintentional overdoses from prescription painkillers quadrupled since 1999, according to the National Institute on Drug Abuse.

A survey from NIDA found that 91.8 million people, roughly one in three Americans, used opioid painkillers such as Vicodin and OxyContin in 2015.

President Trump declared the national opioid crisis a “state of emergency” on August 10 and vowed to “fight the deadly epidemic.”