Preliminary tests by federal investigators have confirmed fears that a deadly synthetic drug nearly 50 times stronger than heroin has arrived in the Upper Midwest — often with fatal consequences for users.

Narcotics seized after a series of overdose deaths last month in the Fargo-Moorhead area — first thought to be heroin — instead turned out to be nearly all fentanyl, federal authorities say. It’s the second time in a decade that synthetic opioids like fentanyl, ordinarily used in medical settings to treat severe pain, have emerged from clandestine drug labs to sweep across the United States.

Now law enforcement and health care officials worry that synthetic versions of fentanyl, which can be added to heroin to boost its potency or passed off as high-strength heroin to unwitting addicts, will inflict a new round of deaths among both longtime addicts and younger users drawn into the opioid epidemic in recent years. Reports of fentanyl use cropped up in other parts of the country last year, but until recently it hadn’t been reported in Minnesota, where the Twin Cities is considered a transshipment point for narcotics.

“I think we’re in the storm now,” said Kent Bailey, assistant special agent in charge at the Minneapolis office of the U.S. Drug Enforcement Administration.

At first, authorities hesitated to sound the alarm — fearing that it would simply advertise a narcotic whose deadliness, for some, is itself a selling point.

But now officials in Minnesota and North Dakota have decided it’s worth the risk because people should know that the heroin now available is more potent than ever, and may not even be heroin.

Graphic: Narcotics' rising toll Graphic: Narcotics' rising toll

“We are advertising: There is something extremely dangerous out there,” said Fargo Police Chief David Todd.

A lab in Mexico

Fentanyl use last exploded in the United States from 2005 to 2007 — killing roughly 1,000 people, primarily in Midwestern and Eastern states, including a rash of deaths in the Twin Cities. A St. Paul man was sentenced to life in prison in 2007 after being found guilty of charges that included conspiracy to distribute fentanyl and crack cocaine.

Agents linked much of that clandestine fentanyl to a single lab in Mexico. Once it was dismantled, the crisis eased — for a time.

Fentanyl alerts from the DEA and the U.S. Centers for Disease Control and Prevention began to circulate again in recent years, but as recently as late 2014, Minnesota had not been mentioned.

Clues that synthetic versions of fentanyl had entered the Twin Cities drug pipeline began to surface late last year. Toxicology officials began noticing overdoses that required unusually high doses of nalaxone, an antidote that can reverse the effects of heroin overdoses. Marvin Seppala, chief medical officer at the Hazelden Betty Ford Foundation, noted a surge in relapses not long after word spread among patients that something lethal was again on the streets.

“They know that this is stronger than anything they ever had because people are dying,” Seppala said. “They hear about the deaths and they flock to it.”

Spoons and bottlecaps

Until recently, fentanyl abuse occurred primarily when the pharmaceutical form — liquid or patches — was stolen from hospitals and other health care facilities, said Carol Falkowski, former director of the alcohol and drug abuse division at the state Department of Human Services who is now with the private Drug Abuse Dialogues.

But now, she said, “criminal organizations are taking advantage of the seemingly insatiable appetite Americans have for drugs.”

In an emergency move to classify and restrict two new synthetic versions of fentanyl last month, the DEA noted reports of it in Minnesota in 2014 and North Dakota and Wisconsin in 2015. Agents seized fentanyl in tablet and powder form and found traces on bottlecaps in spoons, suggesting the synthetics were used as a replacement for heroin or other opioids.

Agents suspect that drug cartels have turned to fentanyl now in an effort to further flood a booming drug market.

Between 2011 and 2015, seizures of heroin by state and local authorities in Minnesota climbed from 8 pounds to 18 pounds — the equivalent of about 82,000 “doses.” The DEA reported seizing an additional 112 pounds in Minnesota from 2013 to 2015.

Deaths are also on the rise. In 2010, the local DEA office began compiling reports from medical examiners in eight Minnesota counties. Overdose deaths attributed to heroin jumped from 16 in 2010 to 73 by 2012. Since 2013, those counties have reported an average of more than 83 deaths a year.

“This nationwide epidemic seems to be far more prolific than the one 10 years ago,” Bailey said. “Our heroin addicts are now 20-year-old kids. … Today’s addicts, many don’t look like your Keith Richards stereotype. They look like your prom queen.”

Much of the heroin, and the supply of adulterants, is flowing directly up Interstate 35 from Mexico or coming from gangs in Chicago or Detroit, authorities say. What’s found in Fargo probably first passed through the Twin Cities.

“You can take it 100, 200 miles north and double your money,” Bailey said.

‘Brave new world’

Fentanyl is easier to produce in a lab than heroin or cocaine, and fentanyl pressed into pills and passed off as drugs like Xanax or oxycodone is also circulating in states from California to Ohio.

Last year agents dismantled an international ring that trafficked fentanyl from Canada and China into the United States, indicting six suspects in North Dakota for a scheme linked to the overdose deaths of two Grand Forks teens. Also last year, the U.S. attorney’s office in Minnesota indicted nine members of a group that called itself the Chicago Crew on charges of conspiracy to distribute heroin, saying the group funneled the narcotic from Chicago to the Twin Cities, sometimes laced with fentanyl “to give their customers a stronger high.” Agents tied at least one death to drugs distributed by the group.

Since Andrew Luger became U.S. attorney for Minnesota in 2014, his office has brought at least 25 indictments, charging more than 100 defendants with trafficking heroin and other drugs. But take down one ring, agents say, and another is ready to inherit its turf.

For Minnesota health professionals, this is “sort of a brave new world,” said Travis Olives, a toxicology fellow with HealthPartners.

Fentanyl and its synthetic relatives attack the respiratory system more rapidly than heroin, he said, creating a smaller window for antidotes. And because new synthetic narcotics keep emerging — the DEA has identified at least 15 for fentanyl — drug authorities and health officials are forced constantly to play catch-up.

“It’s hard to say what we will see tomorrow,” Olives said. “The supply’s always changing, and the adulterants are presumably always changing as well.”

Twitter: @smontemayor