Across the United States, a major health crisis is gaining momentum.

In homes and offices, on street corners and in frat houses and inside middle schools, Americans are overdosing on opioids.

Today, more Americans under the age of 50 are dying from drug overdoses than from any other single cause, according to a new report by The New York Times. More than half a million have already died over the past 15 years, and the pace is still picking up.

America’s drug epidemic is rapidly spreading in plain sight.

Last year, there were 20% more overdose deaths than 2015, according to the Times’ analysis of state death records from 2016. Many of those deaths are attributed to opioids, the addictive family of drugs that includes heroin.

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And the epidemic is hitting America’s poor harder than any other group, according to the US Centers for Disease Control (CDC).

The crisis began unfolding in the 1990s as doctors began prescribing prescription pain medication they were told was not addictive to patients complaining of chronic pain. Soon, many users were hooked. Last year more than 95 million Americans used prescription painkillers, according to the Times.

Since prescription medication in the US can be expensive, many users who became hooked on opioids turned to cheaper alternatives including heroin and its synthetic replacements, like fentanyl, which have flooded the illegal drug market in recent decades, produced and distributed by Mexican drug cartels. The illicit drugs have increased in potency, creating more dependent users.

Now, more than 2 million Americans are believed to be dependent on opioids, according to the Times. And as the epidemic has grown, the drugs have become stronger. The deadliest of the synthetic heroin replacements now is carfentanil, an elephant tranquilizer 5,000 times stronger than heroin.

The anti-overdose drug naloxone, which if administered during an overdose can save a life, is becoming less and less effective in the face of increasingly-powerful opioids, according to the report.

The Times called the epidemic “a modern plague.”

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And that plague it taking its toll on poorer Americans.

The CDC has reported that states with higher poverty levels have higher rates of addiction. And a decade’s worth of data from 2002 to 2013 found that heroin use increased the most among groups with lower income, increasing 77% among those earning $20,000 to $49,000 a year, and 62% in those earning under $20,000 a year, though it has skyrocketed across all income groups in the US.

Low-income patients may have less access to healthcare because of its prohibitively high expense, so that as a prescription for opioids runs out, patients may turn to cheaper, illicit drugs to avoid withdrawal.

Low-income patients may also have more limited access to addiction treatment programs, which can be prohibitively expensive for those without insurance or whose insurance won’t pay for treatment, MaryBeth Musumeci of the Kaiser Family Foundation, told Global Citizen.

About 30% of addicted Americans use Medicaid to pay for treatment, but Medicaid only pays for treatments in states that have opted into former President Barack Obama’s expansion of the program under the Affordable Care Act, according to the Kaiser Family Foundation.

If Congress passes the current replacement bill for the ACA, the American Health Care Act, and reduces Medicaid funding by some $800 billion, it would dramatically affect whether addicts are able to afford treatment, Musumeci said.

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In 2016, states along the East Coast, including Maryland, Florida, Pennsylvania, and Maine, had the largest increase in overdose deaths in the country, according to the Times. Ohio, which also had high overdose rates, last week sued five drug companies for their role in allegedly abetting the epidemic.

In 2015, Nobel Prize-winning economists Angus Deaton and Anne Case identified what they saw as an alarming trend among working-class white Americans without higher education: their death rates were increasing because of an increasing number of what they called “deaths of despair.” The category included death by suicide, alcohol and drugs.

They found that those who had low education rates also reported higher pain and worse health, as well declining wages and increasing financial stress.

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For Americans struggling with pain, access to healthcare, and a dim sense of their futures — plagued by unemployment, low wages, and a lack of hope — opioids seem to have held some promise of pain-management and escape.

The AHCA is currently in the Senate after passing the House of Representatives by one vote last month.

Now, however, the country is in the grips of a deadly epidemic that is hard to curb, as Congress considers withdrawing federal dollars that help the poorest access treatment and healthcare.