The man in the Mickey Mouse shirt was clinging to a light pole on H Street NE when police showed up, and then he dropped his pants. Another man near Eastern Market was laughing so hard that paramedics had trouble keeping him on a stretcher. A third, whom police found prancing through Capitol Hill, started kicking and screaming when eight police and fire officials tried to restrain him.

Paramedics rushed all three men to hospitals in separate incidents Thursday night, and all three said they had taken ­synthetic drugs — a set of substances so alarming to District authorities that Police Chief Cathy L. Lanier recently likened them to crack cocaine in their propensity to induce violence and death.

Synthetic drugs have been around for years. Also known as “synthetic cannabinoids,” the term encompasses a range of mind-altering chemicals that are constantly evolving and are marketed in wildly divergent ways, sometimes as marijuana substitutes on the streets and as incense in convenience stores.

Authorities say the problem spiked in June, with a sudden rash of 911 calls. And they are blaming the drugs for a growing list of frightening incidents across the city. Officials have linked the drugs to two homicides, including a grisly Fourth of July killing in which an allegedly high man stabbed a Metro rider nearly 40 times on a train. D.C. Mayor Muriel E. Bowser (D) said last week that the drugs constituted a “serious threat to our public health and public safety.”

Comparing the effects of synthetic cannabinoid and marijuana

But links between the drugs and violence are almost entirely grounded in anecdotal evidence rather than hard data. Because the mixtures change by the batch in part to skirt drug laws, the drugs are difficult to test — and overdoses are difficult to treat.

Authorities said they’re still testing the Metro stabbing suspect for signs that he was using synthetic drugs, which they say they suspect from his behavior. And a Department of Health spokesman said the agency had yet to collect statistics on overdoses or deaths linked to the chemicals. Even as Bowser signed a new law last week raising penalties for stores caught selling, her health chief acknowledged that testing wouldn’t become available to area health providers until the following week.

The truth about synthetic drugs, law enforcement officials and scientists say, is that the danger lies in the mystery. “Synthetic drugs” don’t refer to a single substance but to a multitude of combinations concocted in laboratories that federal investigators say are mostly in China.

The active ingredients are so shifting in form — the U.S. Drug Enforcement Administration has tracked more than 300 iterations in less than a decade — that no one can say definitively what effect they have on users or those around them.

Nonetheless, there is a growing sense that those effects are worsening in the District, where police, paramedics and even users say that synthetic drugs are becoming more prevalent, causing more overdoses and leading to more violence.

‘We see this every day’

Those same first-hand observers described dozens of incidents. Reactions, they said, range from a blank, zombielike stare to twitchy agitation and unconsciousness.

Lanier has described seeing three people overdose at a notorious strip of pavement near Bladensburg and Benning roads NE in a single hour — “people completely disoriented, disconnected and unconscious, sometimes in the middle of the street.”

On a recent evening at that intersection, about three dozen people had spread across the sidewalk in various stages of consciousness. Some clustered under trees, as they smoked and passed cigarettes between them. Others slumped over concrete tables and benches. A few approached a tall man on a bench and asked if he had the “good stuff.”

“We see this every day,” said one D.C. police officer who was on the scene, referring to a man clinging to a utility pole.

Some people become amorous on the drugs, said another veteran paramedic. Others become angry and sometimes violent. “The scary part is you never know what you’re going to get,” said Capt. Angel M. Lewis, a 20-year veteran paramedic who was able to coax the man away from the utility pole after he had pulled down his pants.

The man gripped by hysterical laughter near the Eastern Market Metro appeared to experience a “happy high” at first, Lewis said. But when they cornered him he screamed uncontrollably, and when they lifted him into the ambulance, he began chewing through his restraints.

The dancing man on Capitol Hill was clearly high, but “he didn’t appear violent at all,” said a woman who was sipping wine with two other residents of a corner rowhouse as spectators applauded a soccer match across the street.

Lewis approached, pleading with the man to let her take his blood pressure and prick his finger to test his blood-sugar level. He walked to her supervisor’s vehicle, a red Chevrolet Tahoe, and sat on the back bumper, the police officer at his side. “Did you do any drugs tonight?” Lewis asked. “K2?”

The man, in his mid-30s, told her he had smoked a full pack of a synthetic drug called Bizarro. He then fought her and others’ attempts to get him on a stretcher, and then he lay on his back in the middle of the street.

“They can go from half asleep to combative and raging,” said Holly O’Byrne, a paramedic who said some patients have been found nearly unconscious, and one recently tried to bite off a colleague’s finger. “The drug is a game changer.”

The worst part of the epidemic, officials say, is that the concoctions appear to keep changing. Several said they have seen signs recently of a more dangerous offering known as Trainwreck that combines synthetic drugs with heroin and PCP. First responders say they suspect some users are mixing the synthetics with prescription mental-health medications.

True effect is unknown

Data obtained by The Washington Post show that emergency room visits for synthetic cannabinoids — commonly referred to on the street by such names as K2, Spice, Scooby Snax and Bizarro — have grown steadily since 2013.

Then came June, when D.C. paramedics recorded 439 ambulance trips — roughly 15 per day — representing more than eight times the number of emergency room visits made for synthetic drugs during the same period last year.

So far in July, ambulances have carried suspected synthetic drug users to the hospital 149 times, and that number is expected to rise. On the most recent date of data collection — July 12 — District ambulances picked up 22 people believed to have used the drugs.

The problem appears less acute in the District’s suburbs, officials say, though Montgomery County officials reported a potential link between synthetic drug use and violent crime and suicide. DEA officials say the prevalence — and deadliness — of the drugs have fluctuated for years across the country.

In the past, the drugs appeared designed to provide a legal high that would subvert state bans on marijuana while inducing similar effects. As laws were passed to target the new chemicals, manufacturers altered their products to stay one step ahead. It has worked — with consequences not only for enforcement but for medical care.

“You’re talking about a poison,” said Andre W. Kellum, the assistant agent in charge of the DEA’s Washington Field Division. “Any time you have people dying, it becomes an issue. And now, having seen it the past few months, people dying from this substance, it opens your eyes. Just like we don’t know the compounds, we really don’t know the true effect of what can happen to every individual that takes it.”

Paramedics say that a violent synthetic-drug user might not respond to sedatives the way a PCP user would. And doctors with proven success reviving victims of heroin overdoses with Naloxone can be stymied by synthetics.

Eric Wish, an associate professor and director of the Center for Substance Abuse Research at the University of Maryland, said researchers “are receiving constant reports of people showing up in emergency rooms with all sorts of bizarre symptoms.”

Because doctors know so little about the chemicals involved, the users are effectively “playing Russian roulette with their bodies,” Wish said.

According to DEA officials, the chemicals are often intentionally mislabeled, for example as “white paint powder,” when they arrive from China. American manufacturers then mix them with acetone and spray them onto leaves.

The drugs are packaged and sold as “incense” or “potpourri” in colorful packets featuring cartoon characters. They’re easy to come by on the Internet. One Web site boasts “the most advanced scientific product available” — offering, for instance, 20 grams of Scooby Snax for $34 and 250 grams of Bizarro for $432.90.

In the Washington area, local gas stations and convenience stores often sell the drugs in smaller packets for $5. On the street, a single rolled cigarette can sell for $2. There is no telling how one packet differs from another with the same label.

“They are being marketed as a legal high,” said Joshua Wansley, who works intelligence in the DEA’s Washington office. “The implicit message is that it’s safe.”

Nearly impossible to police

One way manufacturers have been able to exploit loopholes in the Controlled Substances Act is by marking packages “Not for human consumption.”

D.C. Police officials say it’s nearly impossible to charge a person for possession of a substance that takes so long to test and often isn’t detectable. Users, too, say they smoke the synthetic substances instead of other drugs precisely so they can pass a drug test.

One 38-year-old homeless man said he was arrested two months ago for possession but was promptly released when police realized they didn’t have much of a charge. “Some people use it so they can get jobs,” he said.

In one of the few studies of synthetic drug use, Wish at U-Md. found that out of a sample of parole and probationers who had tested negative for traditional drugs, half had positive results when tested for a panel of synthetics.

In February, Rep. Mac Thornberry (R-Tex.) introduced a bill that attempts to eliminate some of the existing loopholes by broadening the terms of the Controlled Substances Act.

In the District, officials have launched a new offensive to cut down on the supply by going after the businesses that sell it — often liquor shops and convenience stores in poor neighborhoods.

In the past year, the U.S. attorney’s office has targeted at least five businesses and their workers or owners for selling synthetic drugs inside the District. Last week, the D.C. Attorney General’s Office and police temporarily shuttered two stores, including one owned by a retired police officer, that they said were selling synthetic drugs.

Grant Smith, the deputy director of national affairs at the Drug Policy Alliance, which advocates for liberal drug policies, believes that linking the drugs to violence, as city officials have done, could ultimately prove misleading and counterproductive.

“We should be focused more on other types of services — treatment services, and having a better understanding of what these substances are,” Smith said.

But Wish said the synthetic drugs are so dangerous that something needs to be done quickly to stem their use with or without a firm grasp of the chemistry.

“You have to get people’s attention, and if linking it to violence gets people’s attention, then I think it’s worth it,” Wish said. “This is an incredibly dangerous substance.”