America's latest drug epidemic isn't taking place in back alleyways or squalid houses in urban city centers. The new drugs of choice, strong substances made, packaged, and sold by amateur chemists under brands like "Ivory Wave," ''Vanilla Sky" and "Bliss," are for sale in broad daylight, in regular stores for as little as $15.

Over the past two years, the U.S. has experienced a surge in the use of synthetic drugs made of legal chemicals that mimic the dangerous effects of cocaine, amphetamines and other illegal stimulants. These drugs are sold at small, independent stores in misleading packages similar to common household items like bath salts, incense and plant food. Despite their harmless-looking packaging, these substances are powerful, mind-altering drugs that have been linked to bizarre and violent behavior across the country.

On July 10, President Barack Obama signed a bill banning the use, sale, production and possession of more than two dozen of the most common drugs generically referred to as "bath salts." But health professionals say lawmakers are struggling keep up with bath salt producers, who constantly adjust their chemical formulas to construct new synthetic drugs that aren't hindered by new laws.

"The moment you start to regulate one of them, they'll come out with a variant that sometimes is even more potent," said Dr. Nora Volkow, director of the National Institute on Drug Abuse.

U.S. laws prohibit the sale or possession of all substances that mimic illegal drugs but only if federal prosecutors can prove that they are intended for human use. People who make bath salts work around this by printing "not for human consumption" on nearly every packet.

But Barbara Carreno, a spokeswoman for the Drug Enforcement Agency, said the intended use for bath salts is clear.

"Everyone knows these are drugs to get high, including the sellers," she said.

Experts who have studied the problem, estimate more than 100 different bath salt chemicals are in circulation around the country.

Mark Ryan, director of the Louisiana Poison Center, says so many different drugs exist that it's almost impossible to know what people have ingested, or how long the effects will last.

"Cocaine is cocaine and meth is meth," he said. "We know what these things do. But with these new drugs, every time the chemist alters the chemical structure, all bets are off."

The most common bath salt drugs, like MDPV and mephedrone, were first developed in pharmaceutical research laboratories, although regulators never approved them for medical use. During the last decade, they became popular as party drugs at European raves and dance clubs.

The financial lure for small-time drug-makers is enticing. The drugs can be cheaply imported from China or India, and then easily packaged under local brands. For example, bath salts sold in Louisiana carry regional names like Hurricane Charlie or Bayou.

The most dangerous synthetic drugs are stimulants that affect levels of both dopamine and serotonin, brain chemicals that affect mood and perception. People who smoke or snort the powder-based drugs, may experience a surge in energy, fever and delusions of invincibility.

In April, Police officers discovered a package of "Lady Bubbles" bath salts on Sgt. David Franklyn Stewart after the soldier shot and killed his wife and himself during a car chase near Olympia, Wash.

The wild ride began when Stewart sped past a patrol car at 6 a.m. The state trooper followed for 10 miles and reported seeing the driver raise a hand to his head, then heard a shot and saw the driver slump over. The following day, police found the couple's 5-year-old son dead in their home. He had been suffocated with a plastic bag at least 24 hours earlier.

Law enforcement officials believe the bath salts caused Stewart's bizarre behavior and deadly rampage.

Dr. Sullivan Smith, who works at Cookeville Regional Medical Center in Tennessee, said people who come to the hospital after taking the drugs become combative, and it can take four or five health professionals to subdue them. The Tennessee hospital has treated 160 people suspected of taking bath salts since 2010.

Smith recalls one man who had been running for more than 24 hours because he believed the devil was chasing him with an ax. By the time police brought him to the hospital, he was dehydrated and covered in blood from running through thorny underbrush.

"We're seeing extreme agitation, hallucinations that are very vivid, paranoia and some really violent behavior, so it's a real crisis for us," Smith said. "We sedate the living daylights out of them. And we're talking doses on the order of 10 or 20 times what you would give for a painful procedure."

In one of the most highly publicized cases attributed to bath salts, a Florida man attacked a homeless man, stripping him naked and chewing off half his face. Police had to shoot the attacker twice to get him to stop. Although the coroner found no evidence of known bath salt drugs in the man's system, police still suspect some previously unknown combination caused the man's disturbing behavior.

Those on the front lines say legislation outlawing the drugs is a good start. But they don't expect new laws to dramatically curb use of bath salts in the near term.

"The problem is these drugs are changing and I'm sure they're going to find some that are a little bit different chemically so they don't fall under the law," Smith said. "Is it adequate to name five or 10 or even 20? The answer is no, they're changing too fast."

The Associated Press contributed to this story.