Racial bias by doctors may explain why whites are far more likely to get addicted to prescription opioids, a leading expert said.

Research shows that doctors are far less likely to prescribe prescription opioids to their black and Latino patients, making them less vulnerable to develop an addiction to those drugs, said Dr. Andrew Kolodny, the co-director of opioid policy research at the Heller School for Social Policy and Management at Brandeis University.

“[We know] that doctors prescribe narcotics more cautiously to their non-white patients,” he said on NPR on Saturday. “It would seem that if the patient is black, the doctor is more concerned about the patient becoming addicted, or maybe they’re more concerns about the patient selling their pills, or maybe they are less concerned about pain in that population.”

“But the black patient is less likely to be prescribed narcotics, and therefore less likely to wind up becoming addicted to the medication. So what I believe is happening is that racial stereotyping is having a protective effect on non-white populations,” Kolodny added.

Doctors are more likely to prescribe opioid medications to white patients, multiple studies show. A 2016 study found “significant racial-ethnic disparities” in opioid prescriptions for patients discharged from emergency rooms, “with non-Hispanic Blacks being less likely…to receive opioid prescription at discharge for back pain and abdominal pain…compared to non-Hispanic whites after adjusting for other covariates.” Another 2016 study found that blacks are "systemically undertreated for pain relative to white Americans” by medical students and residents.

Over the last year, the recent opioid epidemic has garnered headlines across the country. In 2015, drug overdose was the leading cause of accidental death in the United States, with 33,091 people perishing from prescription pain relievers and heroin overdoses. Of those deaths, 27,056—or about 82 percent—were white.

Last month, President Donald Trump declared the opioid epidemic a “public health emergency,” but stopped short of calling it a national emergency, which would have triggered significant funding.

But the epidemic has been years in the making: Sales of prescription pain relievers in 2010 were four times those in 1999, while the admission rate for use disorder treatment increased six fold in the same time period.

“We have to prevent more people from becoming addicted to opioids, and that's not lecturing to kids, don't do drugs,” Kolodny told NPR. “More than anything else, that's about promoting much more cautious prescribing so that we don't directly addict patients and so that people don't indirectly become addicted because we've stocked everybody's home with a highly addictive drug.”

This is not the first time the United States has faced an opioid epidemic.

In the 1970s, black and Latino communities faced an unprecedented rise in heroin use and overdoses. Similarly, the crack cocaine epidemic of the 1980s and 1990s mostly affected minorities. However, the response from public officials during these crises was to criminalize drug use and enforce mandatory minimum sentencing laws.

For Kolodny and others, the race of those affected explains the difference in response.

“What…we got from policymakers was a message that we could potentially arrest our way out of the problem,” Kolodny said. “What we got was a war on drugs and a crackdown on crime. What we're seeing now is a very different response now that we've got an addiction epidemic that's disproportionately white.”