The effectiveness of prescription drug monitoring programs, designed to reduce “doctor shopping” for opioids, has varied greatly by state, according to a new study by Columbia University researchers. They also found opioid prescribing rates, after surging in recent years, have stabilized.

The researchers used data from the Drug Enforcement Administration on prescriptions for the seven most commonly distributed opioid painkillers: fentanyl, hydrocodone, hydromorphone, meperidine, methadone, morphine, and oxycodone.

They found from 1991 to 2010, the number of prescriptions for opioids almost tripled in the United States, from about 76 million to almost 210 million. The researchers calculated the average dose of opioids prescribed per person (morphine milligram equivalents, or MMEs), and found that number increase fivefold from 1999 to 2008. In 2007, that number started stabilizing.

Nine states recorded significantly fewer MMEs dispensed after they implemented their prescription monitoring database; 14 states reported no significant change; and eight states experienced significant increases in MMEs dispensed. Colorado had the greatest drop in MMEs associated with their prescription monitoring database, followed by Texas and Wyoming. The largest increase was in Connecticut, HealthCanal reports.

The study appears in Public Health Reports.

In a news release, lead author Guohua Li said prescription monitoring databases administered by state health departments appeared to be more effective than those administered by other government agencies, such as the Board of Pharmacy or the Bureau of Narcotics. Seven states with monitoring programs run by a state health department dispensed almost 18 percent fewer MMEs, compared with states without the program.