The findings are published in Drug and Alcohol Dependence.

There are two classes of prescription opioids: analgesics, or painkillers like Oxycontin (oxycodone), and methadone, which is used to treat heroin addiction but which carries a risk of overdose. Using data from the city's Office of the Chief Medical Examiner for the period 1990-2006, the researchers examined the factors associated with death from prescription opioids versus heroin, which historically has been the most common type of opioid fatality in urban areas.

They found that the increase in the rate of drug overdose was driven entirely by analgesic overdoses, which were 2.7 per 100,000 persons in 2006 or seven times higher than in 1990. Meanwhile, methadone overdoses remained stable, and heroin overdoses declined.

Whites were much more likely to overdose on analgesics than blacks or Hispanics. By 2006, the fatality rate among white males was almost two times higher than the rate among Latinos and three times higher than the rate among blacks.

Deaths were mostly concentrated in neighborhoods with high-income inequality but lower-than-average rates of poverty.

"A possible reason for the concentration of fatalities among whites is that this group is more likely to have access to a doctor who can write prescriptions," says Magdalena Cerdá, DrPH, assistant professor of epidemiology at Columbia's Mailman School of Public Health and the lead author on the study. "However, more often than not, those who get addicted have begun using the drug through illicit channels rather than through a prescription."

Price may also play a role, since heroin costs less than analgesics. Additionally, users of prescription opioids may perceive they are safer than other drugs.

Although methadone overdose rates did not increase overall, fatalities among whites increased almost nine-fold while among blacks decreased by 2%. This shift may reflect a change in the nature of methadone use, from a treatment for heroin addiction to a treatment for chronic non-cancer pain.

The study suggests that the profile of a recreational prescription opioid user is very different from the heroin consumer, with less involvement in street-based forms of drug-trafficking and use of other drugs such as cocaine. Because of the different demographics between heroin and prescription opioid users, a different public health approach is needed to target the latter group, say the authors. "It's a different type of drug with a different profile, and we need a different type of response to it," said Dr. Cerdá.

Over the last 20 years, prescription drug overdoses have risen dramatically in the U. S. By 2006, overdose fatalities exceeded the number of suicides, and by 2009, they exceeded the number of motor vehicle deaths.

Most studies on recreational opioid use have focused on rural areas, which have been hit the hardest by the epidemic, but this study suggests that urban areas are contending with a growing health burden from opioid use.

The authors recommend regulating the aggressive marketing of potent drugs like Oxycontin, controlling over-prescribing of analgesics, and taking stricter measures to regulate sales. They also say there should be more law enforcement measures to identify illicit networks of distribution of these drugs and education outreach for physicians and patients.