WINONA, Minn. – 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 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 salts users who are showing up agitated, delusional and even violent. Law enforcement officers are also reporting struggles to subdue hallucinating users who are fighting imaginary people. Some bath salts users are ending up in psychiatric wards.

“It came on like a freight train,” said Mark Ryan, longtime 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.

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

At least 30 states have banned certain bath salts chemicals, including Maine and Minnesota, but the products remain widely available on the Internet.

“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 on users.

The products are typically sold in powder form and 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.

In September, 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.

In Winona, a college town of 27,000 in southern Minnesota, the bath salts 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.

One former bath salts user, Chris Heckman, 26, 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 online or in stores.

Heckman said he’d been drug-free for “quite some time.” But when someone offered a free sample of the new drug and said it was legal, he decided to try it.

He used 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.

“I’ve never experienced any other drug like this,” he said. “This is complete psychosis.”

Around the country, bath salts are now widely known for the bizarre 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 traffic, yelling and banging on cars, and died of a bath salts overdose.

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. Tests showed both parents had bath salts in their systems.

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 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 challenge emergency room staff, too. Users tend to come in panicked and sweating with pounding hearts and high temperatures, sometimes even cardiac issues. They may be restless, suicidal, paranoid, hallucinating.

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

Even in small amounts, bath salts may affect people differently, experts say. The drug triggers mood receptors in the brain — some which make people feel euphoric and energetic, and others that can trigger depressed or violent reactions.

A Cookeville, Tenn., 14-year-old was so high on bath salts that it took 140 milligrams of the surgical sedative midazolam to calm him, 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.

“It’s a scary epidemic, like a brush fire out of control,” Smith said.