John Simmons said he had been using heroin for only six months or so, having graduated from Percocet when the money for prescription painkillers ran out. He and his wife injected together in their South Philadelphia apartment, as they always did.

"The high was immediate," Simmons said. "Like, my knees started buckling. I went to run to my wife, because she started to fall, and I remember waking up, and the paramedics said, 'Give it up, she's dead.' "

He saved one of the empty bags that killed her. An independent lab contracted by The Inquirer found fentanyl in the residue - another death involving an additive about 100 times more potent than heroin that is showing up around the country, especially here.

At least 50 people died of drugs laced with illicit fentanyl in the first half of 2014, more than double the number for all of last year, according to Philadelphia's Office of Addiction Services. Most were among the 173 overdoses involving heroin or morphine, which are on pace to exceed last year's total.

And while addicts often buy and die in cities, most heartache nationwide is in suburban and rural areas. Two-thirds of the 280 drug overdoses (22 of them fatal) reported this year in Camden involved suburban residents.

Authorities and treatment professionals say the reasons are financial. More than a decade ago, drug companies began heavily marketing new prescription narcotics, establishing pills for every ailment as the new normal.

"Kids start experimenting with pills in their parents' medicine cabinet," said Drew Rothermel, chief executive of Texas-based Origins Recovery Centers and a former executive of Caron Treatment Centers in Wernersville, Pa. "There is an epidemic now in a different social strata than there used to be."

Once prescriptions run out, or a doctor stops writing them, users find that the same drugs on the street are costly, he said. "The replacement is heroin."

To dealers, heroin is a business, and fentanyl is a way to "differentiate your product," Rothermel said.

Fentanyl deadens all pain. In medicinal form, the synthetic opioid had $740 million in sales in the United States last year, 70 percent more than morphine, according to the research firm IMS Health - and that does not count purchases by hospitals, where it is widely used to induce anesthesia.

"Every patient I have taken care of in the last week, I have used this drug," said Jesse Ehrenfeld, an anesthesiologist at Vanderbilt University and coauthor of Pocket Anesthesia, a reference book for physicians.

Because it kicks in in just three to five minutes and lasts from 30 minutes to an hour - both much shorter than morphine - fentanyl is safer than other opioids in the operating room.

When people overdose on opioids, "they have stopped breathing," Ehrenfeld said.

On the street, there is no breathing machine, no anesthesiologist to monitor the dosage. And while some medicinal fentanyl is diverted for illegal use, most of what is used to cut heroin is probably made illegally by major drug gangs in Mexico with no quality control.

"They don't know what they are doing half the time, so they put a much larger amount of fentanyl in the heroin, which can kill any seasoned addict," said David Dongilli, who heads the Drug Enforcement Administration division covering Pennsylvania and Delaware. Three or four grains mixed into the heroin that an addict uses can be fatal, he said.

The deadliest recent year was 2006, when fentanyl was believed responsible for well over 1,000 deaths nationwide, including 269 in Philadelphia. That surge may have ended with the shutdown of illicit labs. The drug began reappearing last year, when the DEA cataloged more fentanyl-laced drug samples from Pennsylvania than any other state.

To medical examiners, opioid overdoses look much the same whether they involve heroin, fentanyl, or prescription drugs such as Vicodin and OxyContin. Deaths believed to have been caused by heroin more than doubled between 2009 and 2012, the Pennsylvania State Coroners Association said. Before last year, however, many counties outside Philadelphia did not screen for fentanyl unless there was a reason to test for it.

Burlington County still does not, a spokesman said. Despite rising heroin deaths in Camden and many drug seizures in which the state police lab found fentanyl, the regional medical examiner, who also serves Gloucester County, began routinely screening just this month.

Fentanyl can be mixed with any drug, but is particularly dangerous with local heroin. "Our heroin is testing between 87 percent and 92 percent purity," Camden County Police Chief Scott Thomson said.

His department has been trying to save lives. Since late May, officers have carried the overdose-reversal drug Narcan and have reported 33 "saves."

Thomson learned from experience not to publicize the "brands" linked to a rash of overdoses because addiction-addled brains hear "overdose" and think "more powerful high." When a warning about a location was sent out during the last fentanyl spike nearly a decade ago, "people flooded the community looking for it."

Others are caught unaware.

Simmons, 34, a former assistant manager at a McDonald's in Andorra, thought he and his 33-year-old wife were getting their regular fix on April 17.

A car crash had left both with painful injuries, he said. When the liability insurance ran out, they could no longer afford painkillers and began snorting heroin, then injecting. But they had tapered off slowly enough to avoid withdrawal, Simmons said, and had not used for two weeks.

"The dealer I normally get it off of was arrested," he said. A man who answered the phone said he was taking his cousin's business, so they used him.

Three $10 bags apiece - "JUST DO IT," the big block letters said, a brand likely gone by now, according to police - were to be "a last hurrah" before getting clean.

Simmons recalls his wife falling, and his legs giving way. The rest he heard from the EMTs: "They gave me multiple shots of the Narcan, and they had to use the shockers because I had no heart rate, nothing."

He says his wife's death got him into treatment.