Nearly a decade after the 2008 financial crisis and with U.S. employment at its lowest rate in years, millions of Americans continue to struggle to make ends meet, according to new data from the Federal Reserve.

While the findings show an overall improvement in financial conditions for most households around the country, they also point to enduring problems. Those range from inadequate retirement savings to evidence of the lethal opioid epidemic that has ravaged the U.S. Among the most troubling signs:

Four in 10 adults couldn't cover an emergency expense of $400, or would have to cover it by selling something or borrowing money

Over 20 percent of adults aren't able to pay all of their monthly bills in full

Over 25 percent of adults skipped necessary medical care in 2017 because they couldn't afford the cost

Three in 10 adults have family income that varies from month to month, and 1 in 10 adults experienced hardship as a result

One-sixth of workers have irregular work schedules imposed by their employer, and one-tenth of workers receive their work schedule less than a week in advance

Less than two-fifths of working adults think their retirement savings are on track, and a quarter have no retirement savings or pension whatsoever

About 20 percent of adults (and a quarter of white adults) personally know someone who has been addicted to opioids

The news isn't all bad. For example, in 2017 more people gave a positive assessment of their economic well-being than in the previous year, a continuing trend since the economy started to recover in earnest in 2012. And the share of people who are finding it hard just to get by has fallen sharply in recent years.

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Still, even as the U.S. continues to show healthy growth, the Fed report is a sobering reminder of what it calls the "economic vulnerability" of many Americans.