Nearly 1 million people were not working because of opioid addiction in 2015, the latest research to show that drug use is having a profound effect on the U.S. economy.

A study released Tuesday by the American Action Forum found 919,400 people between the ages of 25 to 54 were absent from the workforce because they were dependent on opioid drugs, a number that grew each year between 1999 and 2015.

The loss of employees and their productivity during that period cost the U.S. economy $702 billion, or just under $44 billion per year, the study calculated.

“It’s a pretty big drag on the U.S. economy,” said Ben Gitis, who co-authored the study with intern Isabel Soto.

The research showed that the loss of work hours caused the economic growth rate to slow by 0.2 percentage points over the 16-year period. While the average growth rate was 2 percent during that time frame, Gitis said, “estimates suggest, had these workers been in the labor force and not addicted to opioids, the growth rate would have been 2.2 percent.”

Opioids killed more than 42,000 people in 2016, according to the Centers for Disease Control and Prevention.

“Of course the opioid crisis is a major health issue. The overdose fatalities by themselves suggest how big of a problem it is,” said Gitis, director of labor market policy at the American Action Forum, a right-leaning think tank. “But it’s also a major constraint on our economy.”

Gitis’s research builds off that of Princeton University economist Alan Krueger, who estimated in a paper last year that the increase in painkiller prescriptions could have caused 20 percent of the observed decline in workforce participation among men and 25 percent among women. Krueger noted that areas with the highest rate of opioid prescriptions registered huge drop-offs in the number of people in the workforce.

Gitis took national data from 1999 and 2015 and, using Krueger’s assumptions, extrapolated how many people would have been in the workforce if not for opioid addiction.

The analysis shows that more work hours were lost for women — 6.4 billion — than men, who were down 5.7 billion hours from 1999 to 2015.

The trend has persisted even as the economy has rebounded and employers in some parts of the country are struggling to fill vacancies. In some places, employers say it is difficult to find people who can pass a drug test. Some companies are even doing away with them.

“It’s something we hear companies talk about all the time, not being able to have workers pass drug tests and being unable to simply get workers to apply because they know they won’t pass the drug test,” Gitis said. “It was really important that we get a sense of what the magnitude of this could be.”

A previous version of this post incorrectly stated 4 million people were out of the workforce because of opioids from 1999 to 2015. There were nearly 1 million people out of the workforce because of opioids in 2015.