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“Flakka,” a new designer drug luring some young Americans, is even more potent and more addictive than its synthetic predecessors, which long skirted the law, experts say.

On the street, it's also called “gravel” for its white, crystal chunks. In the lab, it's known as a stimulant, part of a chemical class called cathinones, with the amphetamine-like effects of Molly and Ecstasy. In the media it's been dubbed "the insanity drug."

Indeed, flakka has fueled a recent, bizarre a spate of public behavior, all occurring in Fort Lauderdale, Florida. On April 4, a man who had smoked flakka ran naked in the streets, claiming people had stolen his clothes. In March, a man on flakka impaled himself on a spiked fence outside the police station. He survived. In February, a man on flakka tried to kick in the police station door, claiming cars were chasing him.

“This is bad stuff,” said epidemiologist James N. Hall, co-director of the Center for the Study and Prevention of Substance Abuse at Nova Southeastern University in Florida.

“The biggest danger is these are guinea pig drugs and the users are like lab rats.”

Flakka simulates the effects of the khat plant, which grows in Somalia and in the Middle East. Experts say that in high doses, it can cause an “excited delirium,” during which a user's body temperature can rise to as high as 105 degrees. It can also create heart problems like tachycardia and life-threatening kidney failure.

“Some get high and some get very sick and may become addicted," Hall said. "Some go crazy and even a few die. But they don’t know what they are taking or what’s going to happen to them.”

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In 2013 alone, cathinones, created in China and sold over the Internet, caused 123 deaths in Florida, according to the United Way of Broward County Commission on Substance Abuse.

Flakka, which can be crushed and snorted, swallowed or injected, is peddled under many brand names, including the less-potent cathinone, “Molly.” Flakka is often mixed with other drugs like methamphetamine.

Ecstasy or MDMA is a different class of chemical altogether, but Molly, though often touted as “pure” MDMA, is a first-generation cathinone. Because flakka is sold under so many different brand names, including “Molly,” users can be fooled, not knowing the potency of this new synthetic drug.

Flakka is “very dose specific,” said Hall. “Just a little (of it) delivers the high effect. It produces energy to dance and euphoria. But just a little more — and you can’t tell by looking at the capsule or baggie.”

Its name comes from the Spanish word “flaco” for thin. Latinos also use “la flaca” as a clubbing term for a pretty, skinny girl.

Spelled “flakka,” it’s “an eloquent collegial term — a beautiful, skinny woman who charms all she meets,” said Hall. “They give [synthetic drugs] names that are hip and cool and making it great for sales.”

Flakka emerged in South Florida last year, and has been seen in parts of Texas and Ohio, but is still not illegal in many states, according to Hall.

The abuse of synthetic drugs is a well-worn story in the United States — the largest consumer market of illicit drugs, according to Dr. Guohua Li, an epidemiologist and founding director of the Center for Injury Epidemiology and Prevention at Columbia University.

“Each generation is exposed to different drugs of choice,” Li said. “The signature substances and their particular effects become a unique feature of the birth cohort.”

“Designer drugs must stay ahead of the authorities and medical communities to keep their illegal business afloat,” Li added.

In the 1940s, a Swiss chemist synthesized a drug from the ergot fungus and discovered the psychedelic properties of lysergic acid diethylamide or LSD. But in 1966, after Timothy Leary urged a generation to, "turn on, tune in, drop out,” the drug was made illegal.

In the 1980s, the all-night rave scene gave birth to the synthetic drug MDMA or ecstasy, giving users the euphoric high of amphetamines and the psychedelic effects of hallucinogens.

By the 1990s, the scourge of lab-produced meth appeared on the West Coast and increased in popularity throughout a decade.

Synthetic marijuana dubbed K2 or Spice, emerged in 2006, and was eventually banned in 2011.

At the same time, MDMA, which is a phenethylamine, saw a resurgence, but by 2010, synthetic cathinones — “bath salts” and the drug Molly — arrived on the club scene.

But now, use of MDMA has tapered off, due to the growing popularity of flakka, which costs only about $5 a dose.

“It’s emerging as the crack cocaine of 2015 with its severe effects high addiction rate for a low cost,” said Hall. “People are terrified of the drug. It’s because the consequences are so devastating.”