Some people on the streets of New York City recently appeared to be overdosing on opioid painkillers after their breathing slowed and they became lethargic.

Others appeared to be overdosing on crack cocaine, exhibiting agitated and violent behavior.

Experts at the National Institute on Drug Abuse (NIDA), however, say those zombielike streetwalkers were on the same drug: K2, or synthetic marijuana.

In all, the NIDA reported that 130 New Yorkers were hospitalized after smoking the drug that can be purchased over-the-counter at less-than-reputable bodegas.

synthetic drug poisonings

The next day, NYPD officers inspected five retail establishments on the suspicion they were selling K2, but none was found on the premises.

Representatives of the Doe Fund — a nonprofit that helps people with histories of homelessness, incarceration, and substance abuse — held a demonstration around a deli suspected of being a primary source of K2 in the Bedford-Stuyvesant area in Brooklyn.

“What we are seeing now with K2 is exactly what we saw with the crack epidemic in the 1980s,” George McDonald, the Doe Fund’s founder and president, said in a statement.

These cases were only a handful of the estimated 8,000 K2-related emergency room visits in New York City since 2015. It’s been illegal in the nation’s largest city since 2012.

Read more: Legal drugs you can buy online that are just as bad as illegal ones »

K2’s a hell of a drug

Unlike marijuana derived from plants, K2 has been linked to a few deaths.

According to a of 456 synthetic marijuana hospitalizations from 2010 to 2015 by the U.S. Centers for Disease Control and Prevention (CDC), three deaths were recorded during that period.

The first death was a 17-year-old boy who died of a heart attack reportedly after a single hit of K2.

The second was a man who died of “respiratory depression, agitation, and delirium/toxic psychosis” after mixing synthetic cannabinoids and oxycodone.

The third man died of kidney failure after mixing a synthetic cannabinoid, bath salts, and LSD.

The drug causing these medical problems — called K2, Spice, and a variety of different names — are synthetic cannabinoids. The most notable cannabinoid in marijuana is tetrahydrocannabinol (THC), which gives the plant its “high.”

Dr. Jordan Tishler, a Harvard-educated physician who specializes in cannabis medicine, says K2 and similar drugs are also not just one chemical but a series of similar chemicals that can be made in a lab.

“The danger stems from two issues. First, the synthetic versions are over 100 times more potent than the natural THC. This means they stimulate the brain both much more and much longer than cannabis does,” Tishler, the physician in chief at Inhale MD Medical Consulting, told Healthline. “Second, these synthetic cannabinoids are not from the plant so they contain no balancing cannabinoids like CBD that moderate the effects of natural THC.”

What K2 users can experience is the overstimulation of the brain's endocannabinoid system, which is involved in many basic functions throughout our bodies.

Users are likely to experience “wild hallucinations, extreme paranoia that often leads to self-harm, and physiologic derangement such as low blood pressure and racing heart,” Tishler said.

“The short story here is that K2 is not cannabis and should not be mistaken for anything to do with natural cannabis use,” he said. “Cannabis is a safe and effective medicine for many, whereas these synthetic chemicals are extraordinarily dangerous.”

Read more: One family’s personal loss to synthetic cannabinoid »

Looks can be deceiving

While synthetic marijuana may look like real marijuana, the type of cannabinoids used in K2 varies depending on its manufacturer, according to Sam Williamson of Realised Recovery addiction counseling in the United Kingdom.

“For me, the main danger with K2 is that many addicts that I've met seem to consider it as a lesser drug than marijuana,” he told Healthline. “This is often the fault of the manufacturers, who often market K2 as a 'safe' alternative to marijuana. But it is just as addictive and just as harmful.”

Dr. Joseph Lee, medical director of the Hazelden Betty Ford Foundation Youth Continuum, said while experts have known about synthetic drugs for some time, they continue to find new and different variations of the chemicals used in them.

For that reason, they’re attractive to different people for different reasons. Some don’t want their drug use showing up on drug screens while others want a bigger and better high.

“Some are in more rural areas where other more commonly used substances are not as readily available, and some users are definitely younger and cannot access other substances,” he told Healthline. “So the use of synthetic drugs is rather common.”

Read more: If marijuana is medicine, then why can’t we buy it in the pharmacy? »

Lawmakers work to keep up

On July 17, Sen. Chuck Schumer (D-NY) introduced legislation to ban the chemicals used to make this so-called synthetic marijuana.

“We need a federal hammer to nail these toxic concoctions of synthetic drugs before things get worse,” Schumer said in a statement.

This would include adding 22 synthetic substances to Schedule 1 of the Controlled Substances Act where, ironically, authentic marijuana currently resides.

There are currently 15 synthetic cannabinoids categorized as Schedule 1, but enforcement is difficult as new chemical compounds are introduced, according to the NIDA.

“Banning these drugs quickly will help the feds step up their game of whack-a-mole so that we can help stem the tide of synthetic drug use here in New York City and across the country,” Schumer said.

Others, however, aren’t sold on that plan.

Even legalizing traditional marijuana — as some would argue would be a just response in the face of the synthetic poisonings — wouldn’t solve the problem because people always want a bigger and better high, Lee argues.

“I think synthetic drugs are here to stay regardless of what happens to real marijuana. Synthetic marijuana is just one kind of synthetic drug. There are so many forms and classes of compounds that can be hard to keep up-to-date even for scientists and physicians,” he said.

Legislation and drug policy, Lee says, aren’t enough to keep people safe. That comes with prevention, education, and the right messaging.

“Drug dialogues are incredibly complicated because so many people have different experiences and opinions about them,” he said. “In our polarized social arena, it's become very difficult to have the kind of important nuanced conversations we need to have.”