By Carolyn Beeler, WHYY

Congressmen Charlie Dent and Pat Meehan were in Philadelphia Tuesday touting a new bill that would make a synthetic drug commonly known as "bath salts" illegal nationwide. It is one of three similar pieces of legislation recently introduced in Congress.

New Jersey just banned the substance, and Pennsylvania is considering doing the same, but drug enforcement officials say keeping ahead of a new class of synthetic drugs will be a challenge.

Bath salts, also called "plant food," are sold perfectly legally online and at head shops, gas stations and drugs stores. They give a high that has been described as a cross between methamphetamine and ecstasy, and can cause paranoia and hallucinations.

Local drug enforcement officials say they are just starting to get complaints about bath salts in Philadelphia, but heavier use has been reported in the Lehigh Valley. Complaints to national poison control centers have been rising.

"Recently we had a man who took a kitchen knife and tried to cut the tattoos off his skin while he was using bath salts," said Dr. Kevin Osterhoudt of the Children's Hospital of Philadelphia.

Osterhoudt said calls to the poison control center at the hospital jumped from four in all of 2010 to about one a day this month. The U.S. Drug Enforcement Administration said it has started the process of adding MDPV, the active ingredient in bath salts, to the controlled substances list, but that might not solve the problem.

"We could act on MDPV, and we may very well," said spokesman Rusty Payne. "But I know for a fact these folks have new chemicals lined up where they change the molecular structure just a bit to evade the law."

Payne said synthetic marijuana started gaining law enforcement attention in the U.S. two to three years ago, but it took until this March for the DEA to even conditionally ban the substance's five most common ingredients.

Legislation could change the legal status of bath salts much more quickly, but Payne said staying ahead of synthetic drugs will take endurance.

"It's going to be a constant battle because there are thousands and thousands of chemicals," Payne said.