The boom of a gunshot jolted Sue Stark out of bed. Did it come from the yard?

Holding her breath as she ran down the stairs to the garage, Stark flung open the door. Her 32-year-old son, Tim, calmly came inside clutching a Winchester rifle. She grabbed the gun and called 911.

"Can't you see them? There's people messing with my car," she remembers him saying as he paced from window to window in the living room, flipping on yard lights and peering outside. "There they are."

Sue looked. The dark street was empty.

Stark learned that night in May that her son, who she said had a history of chemical abuse, had taken a man-made substance with the slang name "plant food," better known as bath salts. Of all the new synthetic drugs alarming health and law enforcement officials in Minnesota and across the country, none has exploded into the culture over the past year as quickly -- or as dangerously.

"I have never, ever seen him that bad in my life," Sue Stark said of her son. "He could have killed somebody."

Cheap to buy, easy to find and mistakenly seen by some users as a legal and mostly harmless alternative to cocaine and other stimulants, bath salts have become the source of a new wave of worried calls to poison control centers nationwide. Last year, those centers received about 300 calls about the synthetic drug.

Already this year, they have logged more than 4,700.

Emergency room doctors, meanwhile, are being forced to take extreme steps to treat some bath salt users who are showing up at hospitals intensely agitated, delusional and even violent. Law enforcement officers are also reporting struggles to subdue hallucinating users who are fighting imaginary people. Some bath salt users are ending up in psychiatric wards.

"It came on like a freight train," said Mark Ryan, long-time poison center director in Louisiana, where the bath salts craze hit early. Bath salts often seem to cause scarier hallucinations than LSD, Ryan said, and sometimes provide the super-human strength of PCP. Far more users experience severe effects compared to other drugs, he said.

"It was just creating havoc for us," Ryan said. "It's not like it's just a bad drug, it's like a superbad drug."

'All over the place'

Bath salts first appeared in the United States in 2009, according to the U.S. Drug Enforcement Administration (DEA). The drugs are so new that federal agencies are still analyzing their toll, but research conducted by the Star Tribune indicates the products have been confirmed or suspected in more than 15 deaths nationwide.

At least 30 states have banned certain bath salt chemicals, including Minnesota, but the products remain widely available on the Internet. Despite their name, the drugs are far different -- and far more expensive -- than ordinary bath products.

"The availability is so all over the place ... that's why it's getting so popular," said Dr. Akikur Mohammad, an assistant clinical professor in psychiatry and behavioral sciences at the University of Southern California. He is studying the effects of bath salts in people.

The products are typically sold in powder form in plastic or foil packages and sold under various names, including Bliss, Ivory Wave and Vanilla Sky. The drugs are usually snorted but can also be smoked, injected or swallowed, according to the DEA.

Like cocaine and other stimulants, bath salts initially might make people feel energized and happy longer than other drugs, experts said. When the initial high dies down, users take more and can end up addicted, hallucinating, panicked and violent.

Chemical components of bath salts can vary. Typically they contain one of several man-made substances related to the illegal khat plant, a popular stimulant in East African countries. Bath salts come from rogue chemists all over the world and have been sold for $40 to $140 a gram. The effects of taking them can differ greatly, experts say, sometimes mimicking ecstasy, cocaine or methamphetamine.

"It is weird that the same brand name applies to such different chemicals," said Mark A.R. Kleiman, a University of California, Los Angeles, professor who studies drug policy. "That just strikes me as odd, and I think sort of unprecedented."

Before bath salts became a problem in the United States, they found popularity in Europe. The United Kingdom banned the bath salt drug mephedrone in April 2010, but a study published in the Journal of Substance Use found that it remained popular in two London clubs last year, second only to cocaine.

In the United States, there is little doubt about the popularity of bath salts. So far this year, the number of bath salt calls coming into poison control centers is twice the volume of heroin-related calls in 2009, the most recent year for which heroin data was available.

Earlier this month, the DEA announced that it intends to temporarily ban three chemicals used in bath salts on an emergency basis, but it is unclear whether the move will significantly impair the business. When the DEA banned five chemicals in synthetic pot earlier this year, manufacturers simply used other substances, according to the Star Tribune's investigation. Congress is also considering a ban on bath salts, as well as other synthetic drugs.

'This is complete psychosis'

In Winona, a college town of 27,000 along the Mississippi River in southern Minnesota, the bath salt epidemic has hit hard this year. At times, authorities have had to deal with as many as three cases a day, Police Chief Paul Bostrack said.

Some of the incidents involving what locals call "plant food" have been startling: One user bit an emergency room doctor, Bostrack said. Another hid in the woods because he thought people were out to kill him. Another saw werewolves.

"Winona has been really hammered with this stuff," Winona County Sheriff David Brand said.

Now, in the wake of Minnesota's July 1 ban on synthetic drugs, Winona police are dealing with fewer cases. They suspect that some bath salt users and sellers have gone underground.

"It's just not as out in the open right now," Bostrack said.

One former bath salt user, Chris Heckman, said that earlier this year the drug was "everywhere" around Winona. Speaking this summer from the county jail, where he was being held on an unrelated offense, Heckman said local people bought it off the Internet or in stores and sold it to friends.

"Everybody thinks they're a drug dealer now," he said.

Heckman, 26, said he had been drug-free for "quite some time." But when someone at a party offered him a free sample of the new drug and told him it was legal, he decided to try it.

He ended up using the stimulants for six months. He said he hallucinated about angels and demons and once swallowed more than 2 grams when he thought that police were coming to get him. He watched as other users ripped their clothes off in search of imaginary surveillance devices, tore walls down and even picked holes into their faces.

"I've never experienced any other drug like this," Heckman said. "This is complete psychosis."

Hallucinations and violence

Around the country, bath salts are now widely known for the bizarre, dangerous effects they are creating.

A Tennessee man high on the drugs threatened to perform surgery on himself, believing something was in his leg. A Florida man walked into Tampa traffic, yelling and banging on cars, and later died of a bath salts overdose.

A couple high on bath salts in West Pittston, Pa., thought 90 people were hiding in their apartment walls. "They were actually ripping the drywall off the walls and trying to stab people inside the walls with large knives," police officer Leonard Lombardo said.

In Washington state, a family wound up dead after the parents took bath salts. Army Sgt. David Stewart, a medic with post-traumatic stress disorder, shot his wife and then himself during a police chase. Authorities later found the couple's 5-year-old son suffocated with a bag tied over his head at their trashed home, where several open packages of bath salts were spotted. Tests showed both parents had bath salts in their systems.

Debbie Spicer, Stewart's mother-in-law, said she believes bath salts prompted the violence. "We are the perfect example of how they destroy people and affect families for life," she said.

In Mississippi, a man high on bath salts shot a sheriff's deputy who tried to subdue him with a Taser. Five men struggled to control him.

"We all got out there and fought with him ... we tried to tie him down with gurney straps ... he just broke them like it wasn't anything," said sheriff's investigator Chris McCallister. "I've messed with people on meth, cocaine, LSD, everything just about, and I've never seen anything like it."

Bath salts cases are challenging emergency room staff, too. Users tend to come in panicked and sweating with fast-pounding hearts and high temperatures, sometimes even cardiac issues. They may be depressed, restless, suicidal, paranoid, hallucinating.

In Bangor, Maine, where bath salts recently swept into town, as many as half of the 10 beds at Acadia Hospital's psychiatric observation unit have been filled with people who had used the drugs, said Dr. Anthony Ng, the unit's medical director.

Even in small amounts, bath salts may affect people differently, experts say. They trigger various mood receptors in the brain -- some which make people feel euphoric and energetic, and others that can trigger depressed or violent reactions based on someone's negative past experiences.

In Cookeville, Tenn., a 14-year-old was so high on the stimulant that it took 140 milligrams of the surgical sedative midazolam to calm him down, said Dr. Sullivan Smith, who is both the town hospital's emergency room director and a part-time police lieutenant. A typical dose used to sedate someone getting wisdom teeth removed is 5 or 10 mg, he said.

"We're seeing phenomenal amounts of sedation required to keep these folks from being violent sometimes," Smith said.

"It's a scary epidemic ... like a brush fire out of control."

'No one's the wiser'

Some bath salt users are much older than the teenagers who have become the focus of public health warnings about the drug. In a recent poison control study of 956 bath salt cases from eight states, the average age of those using the synthetic drug was 29.

One night this summer, a Twin Cities mother in her 20s ducked into a convenience store bathroom in the northern suburbs, locked the heavy steel door behind her and unzipped a Hello Kitty pouch containing a tiny jar of white powder that was labeled "Bliss Euphoric Bath Salts." It was one of several jars she had bought at a local head shop.

The woman, who declined to give her full name and said she worked the night shift as a nurse, was feeling desperate for an energy boost before driving to meet friends at a bar. Resorting to her familiar routine, she ripped the label from the jar, unscrewed the lid and used a cut straw to carefully arrange two pearl-sized dots of powder on it. Then she lifted it to her nose for two quick sniffs.

"That's it," she smiled into the mirror, tilting her face into the fluorescent light to brush residual powder from her lip. "No one's the wiser."

The woman said she first decided to try bath salts after hearing about them on television. Taking just the right amount of the drug made her feel "happy and excited," she said, contending that it's no worse than alcohol -- a point of view that health officials say is a dangerous delusion.

"There's really no point in getting blasted on anything," she said. "I'm a pretty sensible person."

The woman said she avoided using bath salts while working or taking care of her child, and has stopped buying the drug since Minnesota's ban took effect. Now, she said, she drinks cup after cup of coffee.

Voices in his head

Doctors worry that users who repeatedly abuse bath salts could suffer long-term damage.

Alex Seaton is haunted by that idea. Sitting in the Washington County jail, Seaton said voices were still speaking to him 10 weeks after an arrest ended his binge of bath salt use this summer.

"I'm definitely hearing stuff," he said in August, sitting in a jail visiting room with a robe hanging from his thin frame.

Seaton, 19, said he had done various drugs in the past few years, but switched to bath salts because they were legal at the time. He needed to pass drug screenings as he searched for a job, he said.

At first, Seaton said, bath salts made him feel good and talkative. The more he and a friend snorted, the worse things got.

He began thinking the government spoke to him through audio speakers. He saw shadow people. He couldn't stop taking the drugs, constantly thinking, "I wanted more, more, more, more, more," he said. Seaton snorted them in heavy doses for a couple of months and wound up in the psychiatric unit of a hospital.

His older brother, Nick Seaton, saw the change in Alex: "It seems like the bath salts specifically put him over the edge."

The low point came when Seaton's parents were away this summer. He broke into their Cottage Grove house and surrounded himself with loaded guns, according to court documents. Witnesses heard shots one afternoon. Seaton told officers that "voices" made him do it to prevent an alien invasion.

"This stuff is definitely screwing my head," Seaton said during the interview at the county jail, his eyes wide under a mop of shaggy brown hair. "I've never heard voices in my freakin' life until this bath salt."

Staff reporter James Walsh contributed to this report. Pam Louwagie • 612-673-7102