Calling the U.S. drug addiction crisis "the defining public health challenge of our time," former U.S. Surgeon General Vivek Murthy wrote an op-ed Thursday for USA Today laying out exactly how the proposed Republican health care plan will be a disaster for drug treatment.

"Tragically, the American Health Care Act (AHCA) passed by the House would be a major step backward in addressing the addiction epidemic in America," Murthy wrote.

But while the Affordable Care Act (ACA) took steps to ensure that people battling drug addiction could have access to health insurance and, with it, funding for treatment and rehabilitation programs, the Republican replacement plan, the American Health Care Act, will go back on much of this progress.

While the Senate version of the bill, released Thursday morning, makes $2 billion available to states via Health and Human Services grants for "individuals with mental or substance abuse disorders," this likely will have little impact on the problem, and actually reduces the amount of time from the House bill that addiction treatment is funded.

Murthy served under former President Barack Obama from 2014 to 2017. In that time, he wrote for USA Today that he traveled "from Rust Belt cities to remote Alaskan fishing villages, [and] saw the toll of addiction on individual and families who struggled with treatment shortages and the loss of loved ones to opioid overdoses."

While the numbers for 2016 aren't known yet, 2015 was the worst year for drug overdose deaths in American history, and future years are likely to have an even higher death toll.

Murthy cautioned in his op-ed, which was written before the full Senate bill was released, that any money made available for treatment "won't be enough to cover the vast numbers who would lose access to treatment."

Even worse, throwing a relatively small amount of money at addiction while kicking millions off insurance "ignores a fundamental reality that addiction is rarely an isolated condition," Murthy explained. "Many people living with substance use disorders need comprehensive insurance to treat related health conditions like chronic pain, anxiety and depression."

On that score, both the Senate and the House plan likely will make the opioid crisis even deadlier.

In the days before the ACA, "only a third of individual market plans covered treatment for [addiction] disorders," Murthy wrote. The ACA, however, made drug addiction an essential health benefit, meaning it legally had to be covered by all health plans, and there could be no annual or lifetime limit on the amount of money that could be paid out to a patient. Plans simply could not opt out of treating drug addiction.

As ATTN: wrote in previous coverage of the AHCA, the proposed bill "would allow states to waive coverage of essential health benefits for small employer and individually purchased plans." Corporations could then decide to use standards from states that choose to opt out of coverage for a range of services, drug treatment included. Studies have already indicated many companies will opt out, meaning even addicts with employer paid insurance are at risk of losing the ability to benefit from unlimited treatment.

The Senate bill faces a vote where only a few Republicans can defect, so it's not a given that the bill will be passed. But if it is, low-income Americans struggling with opioid addiction will find their situation measurably worse, very quickly.