SEATTLE (AP) - Washington Medicaid patients are nearly six times more likely to die of a prescription painkiller overdose than others in the state, according to a study of death statistics.

The report published Thursday in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report recommends intervening with Medicaid patients who appear to be misusing drugs and keeping closer controls on opioid prescriptions to Medicaid enrollees.

Medicaid is a federal program that pays the medical bills for some low-income and disabled people and is administered by states.

Washington health officials have been looking at the growing number of prescription overdose deaths for several years and noticed low-income populations were at higher risk.

They decided to take a closer look at death certificates for people on Medicaid at the suggestion of someone in Washington's Medicaid office, said Jennifer Sabel, co-author of the study and an epidemiologist with the state Department of Health.

The report offers two possible explanations for the higher overdose deaths among Medicaid patients between 2004 and 2007 in Washington state:

- Medicaid enrollees are prescribed pain medications more often than people not on Medicaid. Sabel said this is probably because people with chronic injuries are often on Medicaid and could need pain medication.

- Medicaid clients are more likely to have substance abuse or other mental health problems. Many of the overdose deaths are caused by a combination of drugs, such as pain killers and antidepressants or pain killers and alcohol.

Sabel said Washington's findings may not indicate a more widespread problem among people on Medicaid in other parts of the country, but it does suggest other states should take a closer look at their own death certificates.

The report also points out that Washington's overall painkiller overdose death rate is higher than the national average. In 2006, the national prescription painkiller overdose rate was 8.8 deaths per 100,000 people. The Washington rate was 10.8 deaths per 100,000 people.

State health officials are taking several approaches toward preventing future prescription poisoning or overdose. They will be distributing a new flyer to doctors across the state for use in educating their patients about the signs and symptoms of overdose.

Medicaid officials in Washington also have improved oversight of clients who have been identified as possibly misusing the system, including people who appear to be "doctor shopping" to increase their access to prescriptions. Those people are now restricted to one doctor, one pharmacy and one hospital for non-emergency care.

"We did look at those particular clients in the study. They are at even higher risk than other Medicaid enrollees," Sabel said.