CHICAGO -- Emergency room doctors are prescribing strong narcotics more often to patients who complain of pain, but minorities are less likely to get them than whites, a new study finds.

Even for the severe pain of kidney stones, minorities were prescribed narcotics such as oxycodone and morphine less frequently than whites.

The analysis of more than 150,000 emergency room visits over 13 years found differences in prescribing by race in both urban and rural hospitals, in all U.S. regions and for every type of pain.

"The gaps between whites and nonwhites have not appeared to close at all," said study co-author Dr. Mark Pletcher of the University of California, San Francisco.

The study appears in today's Journal of the American Medical Association. Prescribing narcotics for pain in emergency rooms rose during the study, from 23 percent of those complaining of pain in 1993 to 37 percent in 2005.

The increase coincided with changing attitudes among doctors who now regard pain management as a key to healing. Doctors in accredited hospitals must ask patients about pain, just as they monitor vital signs such as temperature and pulse.

Even with the increase, the racial gap endured. Linda Simoni-Wastila of the University of Maryland, Baltimore, School of Pharmacy said the race gap finding may reveal some doctors' suspicions that minority patients could be drug abusers lying about pain to get narcotics.

The irony, she said, is that blacks are the least likely group to abuse prescription drugs. Hispanics are becoming as likely as whites to abuse prescription opioids and stimulants, according to her research. She was not involved in the current study.

The study's authors said doctors may be less likely to see signs of painkiller abuse in white patients, or they may be undertreating pain in minority patients.

Patient behavior may play a role, Pletcher said. Minority patients "may be less likely to keep complaining about their pain or feel they deserve good pain control," he said.

Stricter protocols for prescribing narcotics may help close the gap.

In the study, opioid narcotics were prescribed in 31 percent of the pain-related visits involving whites, 28 percent for Asians, 24 percent for Hispanics and 23 percent for blacks.

Minorities were slightly more likely than whites to get aspirin, ibuprofen and similar drugs for pain.

The data came from a well-regarded government survey that collects information on emergency room visits for four weeks each year from 500 U.S. hospitals. The new study was funded by federal grants.

"It's time to move past describing disparities and work on narrowing them," said Dr. Thomas L. Fisher, an emergency room doctor at the University of Chicago Medical Center who was not involved in the study.

Fisher, who is black, said he is not immune to letting subconscious assumptions inappropriately influence his work as a doctor.

"If anybody argues they have no social biases that sway clinical practice, they have not been thoughtful about the issue or they're not being honest with themselves," he said.