TUSCALOOSA, Ala. — Roslyn Lewis was at work at a dollar store here in Tuscaloosa, pushing a heavy cart of dog food, when something popped in her back: an explosion of pain. At the emergency room the next day, doctors gave her Motrin and sent her home.

Her employer paid for a nerve block that helped temporarily, numbing her lower back, but she could not afford more injections or physical therapy. A decade later, the pain radiates to her right knee and remains largely unaddressed, so deep and searing that on a recent day she sat stiffly on her couch, her curtains drawn, for hours.

The experience of African-Americans, like Lewis, and other minorities illustrates a problem as persistent as it is complex: Minorities tend to receive less treatment for pain than whites, and suffer more disability as a result.

While an epidemic of prescription opioid abuse has swept across the United States, African-Americans and Hispanics have been affected at much lower rates than whites. Researchers say minority patients use fewer opioids, and they offer a thicket of possible explanations, including a lack of insurance coverage and a greater reluctance among members of minority groups to take opioid painkillers even if they are prescribed. But the researchers have also found evidence of racial bias and stereotyping in recognizing and treating pain among minorities, particularly black patients.

“We’ve done a good job documenting that these disparities exist,’’ said Salimah Meghani, a pain researcher at the University of Pennsylvania. “We have not done a good job doing something about them.’’

Meghani’s 2012 analysis of 20 years of published research found that blacks were 34 percent less likely than whites to be prescribed opioids for conditions such as backaches, abdominal pain, and migraines, and 14 percent less likely to receive opioids for pain from traumatic injuries or surgery.

Other studies have found that pharmacies in poor but largely white neighborhoods were 54 times as likely than those in poor minority neighborhoods to have adequate supplies of opioids, and that white children with appendicitis were almost three times as likely as black children to receive opioids in the emergency room. Black children were more likely to receive less potent, nonnarcotic medications like ibuprofen and acetaminophen, even after adjusting for pain level and other factors. And new research published this week found that blacks have significantly lower odds than whites of receiving opioids when they visit an emergency room for “nondefinitive’’ back or abdominal pain.

Adam Hirsh, a pain researcher at Indiana University, said that “black and white patients are getting treated differently.’’

He and other researchers say the reasons may include false stereotypes, such as the assumption that blacks are more likely to abuse drugs, as well as a tendency for doctors to empathize less with patients whose race is different from their own — perhaps subconsciously — and to underestimate the severity of their pain. Only about 4 percent of the country’s practicing physicians are black.

Lewis, 50, ended up at a health center in Tuscaloosa, Whatley Health Services, which has clinics in six counties — some predominantly black, others heavily white.

Doctors in Alabama prescribe opioid painkillers at a higher rate than their counterparts in any other state, according to the CDC. Nobody tracks how those prescriptions are allocated by race. But payment data from Medicare, the government program that covers people 65 and older as well as some with disabilities, shows that in all but one of Alabama’s majority-black counties, the rate of opioid prescribing is below the state average. Four of the five Alabama counties with the lowest rates of opioid prescribing for Medicare patients are at least two-thirds black, according to census data.

Dr. Gerold Sibanda, a primary care doctor in rural Greensboro, Alabama, said he viewed unequal treatment of pain in black patients as a real problem.

“I meet patients who are changing doctors because ‘I’m still in pain,’’’ said Sibanda, who works for Whatley Health Services. “And when I ask, sometimes they haven’t been tried on what you would think would be traditional medications — nonnarcotic, even — for whatever their pain is.’’

Dr. Carmen R. Green, an anesthesiologist, pain medicine specialist and University of Michigan professor who has studied treatment disparities for years, said that “the role of race is more important, although race and class often interact.’’

One study, in 2004, found that workers’ compensation programs spent less to treat blacks with lower back injuries, and that the treatment periods for blacks were shorter, regardless of income level.

“Our data pretty clearly say it’s a race issue,’’ said Raymond Tait, a pain researcher at St. Louis University in Missouri and co-author of the 2004 study. “Our take on this was that during active treatment, we believe negative stereotypes impact clinical decision-making.’’