This past month brought a new reminder of the potential lethal effects of heroin addiction.

During a 10-day stretch in Butler alone, five people died of suspected drug overdoses, authorities said.

Toxicology tests are under way to determine whether a bad batch or more of heroin could be responsible for what may be a sudden wave of fatal overdoses to hit Butler.

Authorities suspect but can’t say for sure that the heroin in those fatalities had been cut with fentanyl. Another possibility, they say, is that fentanyl may be getting mistaken for heroin by those using it.

Whatever the reason, the spike in apparent fatal overdoses has prompted an outcry from top law enforcement officials in Butler County and addiction treatment advocates.

“It’s alarming and concerning when we see people overdosing at this rate,” said District Attorney Richard Goldinger. “We don’t know why this is happening but we suspect a more potent batch of heroin is making the rounds.”

One specific additive, which causes a kind of “super high,” could be at play, said county Detective Tim Fennell, who heads the county Drug Task Force.

“We’re seeing a significant number of fatal overdoses linked to heroin and some heroin mixed with fentanyl,” he said.

Fentanyl is a time-release narcotic painkiller that is delivered in a patch or pill. It is purportedly 50 to 100 times more powerful than morphine, according to health experts.

The narcotic kills by overwhelming receptors in the brain, causing respiratory failure, said Linda Franiewski, executive director of the Ellen O’Brien Gaiser Center in Butler. Death is sometimes instantaneous.

Fennell said authorities are working to determine if the rise in suspected lethal overdoses in Butler can be attributed to heroin users experiencing heroin laced with fentanyl.

“It could be fentanyl mixed in with heroin. It could be all fentanyl, or it could be something else,” he said. “We don’t know.”

But in each of the city cases this month, he noted, police recovered syringes and stamp bags of suspected heroin.

“So we know it’s either heroin or fentanyl-laced heroin,” Fennell said.

The apparent fatal overdoses in Butler occurred between May 17 and 27. Among the deaths were two women, ages 46 and 45, both addicts known to police, who died on consecutive days, May 23 and 24.

A 25-year-old woman died on May 17 and a 36-year-old man died on May 20.

In the most recent death, a 42-year-old man died after apparently using heroin. He also had fentanyl patches, authorities said.

Toxicology results of this month’s suspected overdose cases won’t be known for several weeks.

But unlike last year’s scare that had 22 people in Western Pennsylvania, including three in Butler County, die from a single batch of fentanyl-tainted heroin, the five suspected overdose victims in the city this month apparently injected heroin delivered in bags with different names on them.

And in at least one case, there was no name stamped on the bags.

“So we don’t know if the heroin (in the Butler cases) came from a single dealer or not,” Fennell said. “It’s frustrating.”

Butler police Capt. David Dalcamo acknowledged his department has seen an increase in overdoses but he doesn’t know why.

He said police are “looking into some things” in their investigation of the suspected fatal overdoses, but he added that it was “way too early” to draw any conclusions until the toxicology reports are completed.

The uptick in drug-connected deaths appears to be a city phenomenon, according to statistics provided by the county coroner’s office.

The office reported Tuesday, before the most recent case, that so far this year there have been 14 confirmed deaths from drug overdoses. Five other suspected overdose cases were pending.

Those numbers appear to be on par with what the county experienced last year. In 2014, the office reported that 33 people died of drug overdoses.

But Fennell said he fears what is happening in Butler could be a precursor of things to come countywide. And the wild card is fentanyl, either in its pure form or mixed with heroin.

To make his point, he pointed to a pair of overdose deaths last month outside the city.

On April 5, a 25-year-old man died in Slippery Rock Township. A recently received toxicology report listed the cause of death as “fentanyl toxicity.”

Two days after that death, a 52-year-old man on April 7 died in Evans City of combined drug toxicity that included fentanyl and heroin.

“It’s scary,” Franiewski said. “It’s pretty bad. It’s senseless.”

Franiewski said she is aware of the sudden surge of apparent fatal overdoses in the city. She’s alarmed.

“It’s not usual,” she said. “It’s ridiculous. It’s out of control.”

But, she added, it’s not entirely surprising.

Of the individuals seeking treatment services at the Gaiser Center in April, 71 percent were heroin addicts.

“Heroin is completely epidemic in the county,” Franiewski said. “It’s unprecedented.”

She said she believes the increase in heroin use is tied, in part, to the over prescription of opiate-based painkillers like fentanyl.

Heroin also is an opiate. But heroin is cheaper than those painkillers, hence its drug-of-choice status.

Beyond the economic factor that drives users to heroin, Franiewski said, recent state-approved restrictions on prescription opioids have made heroin more accessible than painkillers.

“It’s become very, very common that people who started on opiate painkillers turn to heroin,” she said.

That can be expected, she noted, because they’re chasing the same high with those drugs.

Franiewski said one way to address the growing number of heroin and opioid overdoses is to make the drug naloxone, also known by its trade name Narcan, more accessible to addicts and their families.

Only last month, state police began carrying Narcan in their patrol cars. That move followed legislative action to equip first responders with the lifesaving nasal-spray drug.

Goldinger said his office along with the county sheriff’s office is working to secure funding that would get the same antidote in the hands of municipal police as early as next month.

Thanks to a private foundation grant, the Gaiser Center recently acquired its own supply of Narcan that it soon plans to distribute to “people at high risk,” Franiewski said.

“This stuff really saves lives,” she said.

Education and additional public funding for addiction treatment services and resources, she said, are other ways to combat the opioid-related overdoses.

Goldinger and Fennell said law enforcement also has a key role to play. One way is to attack the source — the drugs as well as the dealers.

Goldinger said police and prosecutors in the county are committed to seeking justice for the overdose victim by trying to find and charge the supplier.

The potential top charge of drug delivery resulting in death, a first-degree felony, can result in a multiple-year sentence for the dealer.

However, filing a case with that charge is not easy, Fennell said.

“That’s because our best witness is dead.”