Federal Reserve Chair Janet Yellen has said widespread opioid abuse in the US is linked to a fall in the number of Americans working or looking for work.

According to the Centers for Disease Control (CDC), prescription drug abuse costs an estimated $78.5bn (£61.5bn) annually. Those costs are related to healthcare, productivity loss and criminal activity, the BBC reported.

More than 90 Americans die each day due to opioid overdoses.

The head of the US central bank said she was unsure if opioid abuse is a cause of the decline in the workforce or a symptom revealing more enduring economic issues.

Yellen added that changes in technology and an ever ageing workforce are also contributing factors.

"I do think it is related to a decline in labour force participation among prime-age workers," Yellen said in response to a question from Senator Joe Donnelly (D-Ind.).

"I don't know if it's causal or if it's a symptom of long-running economic maladies."

According to the BBC, Yellen also noted that the US has seen an unusual rise in the death rate. The US is "the only advanced nation that I know of where in these communities we're actually, especially among less-educated men, seeing an increase in death rate partly reflecting opioid use," she noted.

"It's obviously a very serious and heartbreaking problem," Yellen added.

According to CNBC, the US Bureau of Labor Statistics reports the labour force participation rate has fallen since the Great Recession and stagnated the last four years near 63%.