The average life expectancy in the United States dropped for the second year in a row as the opioid epidemic, recently fueled by a rise in use of fentanyl and other synthetic opiates, continues to scourge the nation, federal officials reported Thursday.

More than 63,600 people died from drug overdoses in 2016, a rate three times that of overdose deaths in 1999, according to the December 2017 report from the National Center for Health Statistics, which is part of the U.S. Centers for Disease Control and Prevention.

Of those lives lost, 66 percent – 42,249 drug fatalities – involved opioids, a 28 percent increase over the previous year, the report says.

Specifically, between 2015 and 2016 the number of people who fatally overdosed on prescription pills increased 14 percent and on heroin nearly 20 percent. Deaths due to fentanyl and other synthetic opiates more than doubled.

Because of these ever-growing rates of overdose deaths, researchers witnessed the average American life expectancy drop another degree, from 78.7 in 2015 to 78.6 in 2016. But the life expectancy in 2015 was already a sobering drop from 2014, when the life expectancy was 78.9.

"For any individual, that's not a whole lot," Robert Anderson, chief of the mortality statistics branch at the National Center for Health Statistics, told NPR. "But when you're talking about it in terms of a population, you're talking about a significant number of potential lives that aren't being lived."

Used as a statistical metric to determine the average time someone or something is expected to live, life expectancy in the U.S. has been rising steadily for decades, with only sporadic downward ticks. The last time it dropped was in 1993, reflecting the AIDS epidemic. Otherwise, it hasn't dropped two years in a row since the early 1960s.

President Donald Trump officially declared the opioid crisis a nationwide public health emergency on Oct. 26. While his pronouncement did not signify additional funding to combat opioids, it labeled the pandemic a top priority for the government and gives the Trump administration and the Department of Health and Human Services the means to move department funding and resources around more easily to address the crisis.