PHILADELPHIA — An estimated 469,000 adults in Philadelphia — nearly one-third of the population — used a prescription opioid like Percocet or OxyContin in the last year, a city survey found, and more than 81 percent of them received the prescriptions from their health care providers.

Of particular concern, the city Health Department said, 168,000 adults said they had taken a prescription opioid in the last seven days, and more than a third of them were also on a benzodiazepine, like the anti-anxiety medication Xanax. The combination of benzos and opioids increases the odds of an overdose.

A dramatic rise in painkiller prescriptions nationwide preceded what is now an epidemic of overdoses. More than 900 city residents died last year from overdoses of heroin, fentanyl and other drugs, a toll that is projected to exceed 1,200 this year.

Most heroin users say they started with prescription pain pills.

“While in the past we’ve primarily reported data on drug overdoses, this survey shows what is truly fueling this epidemic. It’s shocking how many people are using these dangerous, highly addictive drugs, and disturbing that physicians continue to prescribe them so carelessly. Doctors need to prescribe these drugs less often, in lower doses and for shorter durations,” Thomas Farley, commissioner of the Philadelphia Department of Public Health, said in a statement.

The statistics are based on an online survey of 466 Philadelphians conducted between May 9 and June 26.