New Haven emergency personnel respond to overdose cases on the New Haven Green in Connecticut on Wednesday. More than 30 people overdosed from a suspected bad batch of “K2” synthetic marijuana. (Arnold Gold/AP)

The ever-rising death toll from the synthetic opioid fentanyl showed graphically this week how vulnerable the United States has become to powerful drugs concocted in laboratories.

On the same day that more than two dozen people were raced from a New Haven, Conn., park to emergency rooms after violent reactions to synthetic marijuana, federal authorities announced that more than 72,000 people had died of drug overdoses nationwide in 2017. Leading the death toll is the increasing number of fatalities from fentanyl.

“It is the 2.0 of drugs right now, the synthetics,” said Tom Synan, the police chief in Newtown, Ohio.

In an unusual episode involving a batch of synthetic drugs, more than a dozen people fell ill in less than an hour in New Haven’s central park on Wednesday. People lay unconscious. Others convulsed and vomited. First responders could barely keep up, sprinting from person to person; a news conference with the police chief was interrupted by word of another victim and medics rushing to administer treatment. All of those who took the drug survived, and authorities announced an arrest in connection with the incident.

Fentanyl, a synthetic opioid about 50 times stronger than heroin, has ravaged communities across the nation. In this Washington Post original documentary, reporter Wesley Lowery travels to one of the hardest hit cities, Philadelphia, where he finds that despite efforts to deal with the crisis, it's only getting worse. (Video: Whitney Leaming, Reem Akkad/The Washington Post, Photo: Salwan Georges/The Washington Post)

The culprit was synthetic marijuana, a potent drug that has hospitalized hundreds of people in 10 states in recent months. Unlike previous overdose clusters around the country, “there is no indication of the presence of fentanyl” in samples of the synthetic marijuana being analyzed by the Drug Enforcement Administration, said Uri Shafir, acting assistant special agent in charge of the DEA’s New Haven office. Early media reports had indicated the synthetic marijuana was laced with fentanyl.

Illicit fentanyl continues to do far more damage on the streets than other drugs. About 50 times more powerful than heroin, it is cheap and easy to make. It is being cut into heroin, cocaine and other drugs and is often pressed into pill form, tricking users who covet prescription medications. According to one medical specialist in Baltimore, users aware of the combination of drugs they can receive in a single purchase are calling the mixture “scramble.”

More than 72,000 people died of drug overdoses last year, according to preliminary 2017 figures from the Centers for Disease Control and Prevention. That is a 9.5 percent increase from 2016, a rise driven largely by deaths from fentanyl and carfentanil, an even stronger opioid typically used as a large-animal tranquilizer.

Just a few grains of either can kill a person. In Cincinnati, 174 users overdosed in six days in 2016 after taking heroin cut with carfentanil.

For years, much of the focus has been on curbing the supply of illicit opioid painkillers from doctors and pharmacies to people who abuse the drugs. Now, there is some evidence that battle may be succeeding. The CDC data shows that deaths involving hydrocodone and oxycodone appear to have flattened out, offering possible hope that painkiller deaths might have peaked.

On Thursday, the Justice Department and the DEA announced a proposal to further curtail the manufacturing of six powerful prescription painkillers, reducing production quotas by an average of 10 percent in 2019. President Trump also asked Attorney General Jeff Sessions to bring a federal lawsuit against opioid suppliers. The federal government already has filed a statement of interest in a mammoth federal lawsuit involving cities, counties, Native American tribes and unions who have sued companies up and down the opioid supply chain.

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But authorities and others who work with those who are addicted say that prescription pills are no longer the most urgent threat.

“Seventy-five percent of the deaths we get are fentanyl related,” said Al Della Fave, a spokesman for the Ocean County, N.J., prosecutor. “It’s the heroin laced with synthetic opioids that we’re getting creamed with.”

Andrey Ostrovsky, president and chief executive of the Concerted Care Group in Maryland, a chain of three outpatient treatment centers, said positive tests for fentanyl among opioid users during the past three months were in the 30 to 40 percent range. The organization sees about 1,300 people each day.

Much of the nation’s supply of fentanyl is coming in large quantities from Mexico, where it is made by cartels, and from China, where it is made in clandestine labs and purchased on the dark web.

State and federal authorities are cracking down on the drug, with prosecutors more aggressively using laws that hold drug dealers criminally liable for overdose deaths. Sessions has targeted 10 areas of the country to bring charges against anyone dealing fentanyl, regardless of the quantity. The Justice Department has tripled fentanyl prosecutions across the country, seized thousands of kilograms of heroin and fentanyl and brought the first cases charging Chinese nationals with selling large quantities of the drug to Americans.

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Trump on Thursday asked Sessions to look into opioids coming from China and Mexico, saying those countries were “sending their garbage and killing our people.”

But some on the ground said the help is not coming quickly enough.

“I think people aren’t willing to take the tough actions needed to deal with the immediacy of the synthetics. . . . The emergency is stopping the synthetics,” Synan said. He lamented the role of politics in drug policy, which he said has limited progress regardless of which party has been in power.

Keith Humphreys, a professor of psychiatry and a drug policy expert at the Stanford University School of Medicine, said the United States is poorly positioned to have an impact in China’s illicit supply of fentanyl because of the ongoing feud over tariffs between the Trump administration and Beijing.

“They could help us, but they’re not going to,” said Humphreys, who spent a year in the Obama administration’s Office of National Drug Control Policy. The way to enlist the Chinese is “carefully, respectfully, and not on the front page or on Twitter.”

The overdoses in New Haven illustrate other difficulties for authorities: There are numerous synthetic drugs available; amateur chemists often simply tweak chemical compositions to skirt laws and make the drugs available to the public.

Federal officials last month issued a warning about the spread of synthetic marijuana, known as K2, across the country. In recent months, K2 has caused hundreds of people in about 10 states to be hospitalized, sometimes with severe bleeding. Several people have died because of complications. The danger lies in the drug’s unpredictability and its tendency to be cut with potent opioids or an anticoagulant used in rat poison.

“Drug dealers are putting [fentanyl] on the street because obviously it’s more powerful, people get addicted, they make more money,” Synan said. “But on the other end, more people overdose, more people die and it takes a larger response from authorities.”

Correction: An earlier version of this story reported that a few grams of fentanyl or carfentanil can kill someone; the drugs are so potent that just a few grains can be deadly.