One man ran naked through a Florida neighborhood, tried to have sex with a tree and told police he was the mythical god Thor. Another ran nude down a busy city street in broad daylight, convinced a pack of German shepherds was pursuing him.

Two others tried separately to break into the Fort Lauderdale Police Department. They said they thought people were chasing them; one wound up impaled on a fence.

The common element to these and other bizarre incidents in Florida in the last few months is flakka, an increasingly popular synthetic designer drug. Also known as gravel and readily available for $5 or less a vial, it's a growing problem for police after bursting onto the scene in 2013.

It is the latest in a series of synthetic drugs that include Ecstasy and bath salts, but officials say flakka is even easier to obtain in small quantities through the mail. Flakka's active ingredient is a chemical compound called alpha-PVP, which is on the U.S. Drug Enforcement Administration's list of the controlled substances most likely to be abused. It is usually made overseas in countries such as China and Pakistan.

Flakka, a derivative of the Spanish word for a thin woman, is usually sold in a crystal form and is often smoked using electronic cigarettes, which are popular with young people and give off no odor. It can also be snorted, injected or swallowed.

“I've had one addict describe it as $5 insanity,” said Don Maines, a drug treatment counselor with the Broward Sheriff's Office in Fort Lauderdale. “They still want to try it because it's so cheap. It gives them heightened awareness. They feel stronger and more sensitive to touch. But then the paranoia sets in.”

Judging from the evidence being seized by police around Florida, flakka use is up sharply. Submissions for testing to the Florida Department of Law Enforcement's crime labs have grown from 38 in 2013 to 228 in 2014. At the Broward Sheriff's Office laboratory, flakka submissions grew from fewer than 200 in 2014 to 275 in just the first three months of this year, according to spokeswoman Keyla Concepcion.

“It's definitely something we are watching. It's an emerging drug,” said Chad Brown, an FDLE supervisory special agent.

According to the National Institute on Drug Abuse, reports of flakka or gravel also have surfaced in Ohio, Texas and Tennessee, but Florida appears to be the nation's hot spot.

“Synthetic drugs are illegal and present a grave danger to our community, particularly our children,” said Miami U.S. Attorney Wifredo Ferrer.

In one recent case, 22-year-old Jaime Nicole Lewis was charged in a DEA complaint with conspiracy to distribute flakka after DEA agents based in London intercepted U.S.-bound packages of the drug that were made in Hong Kong. An undercover DEA agent posing as a delivery company employee then brought the packages to Lewis' home in Palm Beach County, according to a court affidavit.

Lewis is being held without bail and is due to enter a plea next week. Her attorney, Paul Lazarus, said prosecutors will have to prove she knew the packages contained illegal drugs. A man believed to be the flakka ringleader in this case also is charged, but has not been arrested.

James West, a 50-year-old homeless man, was caught on surveillance video in February trying to kick in the heavy glass front door of the Fort Lauderdale Police Department, finally cracking it with large rocks. Bleeding above one eye, West told officers that he was desperate for help from police because “he was being chased by 20-25 individuals and he didn't know why.” He later told police he had smoked flakka.

In March, Shanard Neely got impaled through the buttocks on the department's 10-foot-high security fence while trying to climb over, convinced he was being pursued and that “he needed to go to jail or they would kill him,” police said. Neely, 37, also told officers he had smoked flakka. It took hours for rescuers to cut him down.

And in Palm Beach County, a SWAT team had to talk Leroy Strothers, 33, off a rooftop in January. He had fired a shot from up there, claiming he was being followed by a gang that had threatened his family. Strothers, who was charged with being a convicted felon in possession of a firearm, told officers he had smoked flakka and could not remember how he got on the roof.

“I'm feeling delusional and hallucinating,” Strothers said, according to a sheriff's report.

The FDLE's Brown said his agency is training police to better recognize flakka and the symptoms it can cause.

One challenge is that flakka manufacturers make subtle changes to its chemical makeup, foiling efforts to test for the drug, and it is frequently mixed with other substances, such as crack cocaine or heroin, with unknown effects, said Maines, of the Broward Sheriff's Office.

With prolonged use over as little as three days, behavioral changes can be severe.

“It actually starts to rewire the brain chemistry. They have no control over their thoughts. They can't control their actions,” Maines said. “It seems to be universal that they think someone is chasing them. It's just a dangerous, dangerous drug.”

The Associated Press