Why You Should Care About GNC's New Supplement Guidelines

— -- After being one of four companies to be accused of selling phony dietary supplements, GNC announced today that it will institute better testing guidelines. But health experts say consumers should still be vigilant when picking out their herbal pills and remedies.

Here's what you need to know:

What happened?

The New York State attorney general sent cease and desist letters to GNC, Target, Walgreens and Walmart in February, barring them from selling store-brand supplements in the state. The attorney general's office noted at the time that it had tested these supplements for plant DNA listed on the bottles, such as echinacea, ginseng and St. John's Wort, as part of an ongoing investigation. The attorney general's office said it found that 79 percent of the products either had none of the plant DNA listed or were contaminated with unlisted ingredients.

"When consumers take an herbal supplement, they should be able to do so with full knowledge of what is in that product and confidence that every precaution was taken to ensure its authenticity and purity," New York Attorney General Eric Schneiderman said today as GNC announced its more stringent testing guidelines.

"When it comes to consumer health, we expect companies to reach a high safety bar. Without tests and safeguards, including those that rule out dangerous allergens, these supplements pose unacceptable risks to New York families," Schneiderman added. "I urge all herbal supplements manufacturers and retailers to join GNC in working with my office to increase transparency and put the safety of their customers first."

GNC and Schneiderman announced today that they had come to an agreement about more rigorous company-wide testing standards that dig deeper into the supply chain. GNC said that further internal and third-party testing has found it to be in line with the U.S. Food and Drug Administration's current good manufacturing practices.

"As our testing demonstrated, and this agreement affirms beyond any doubt, our products are not only safe and pure but are in full compliance with all regulatory requirements," said GNC's CEO, Michael Archbold.

It is the first of the four companies to make such a move, but Walgreens Inc. released the followed statement: "As we said earlier, we take these issues very seriously. We continue to review this matter and also intend to continue cooperating and working with the attorney general of New York."

Walmart weighed in as well: "Walmart has been complying with the New York Attorney General’s legal requests by submitting information and we will continue to work with his office. The specific products called into question were tested by the manufacturers during and at the end of production and the results confirmed that the ingredients on the label were present and the products were not adulterated."

Target did not respond to ABC News' request for comment.

Why are supplements different from other drugs?

Clinical dietitian Lisa Cimperman, who works at U.H Case Medical Center in Cleveland, Ohio, said consumers should remember that dietary supplements are not subject to the same safety and efficacy testing as drugs.

A 1994 law called the Dietary Supplement Health and Education Act made supplement manufacturers responsible for safety and proper labeling -- not the FDA. The FDA does not approve these supplements before they hit shelves, according to the agency's website.

"We don't know that anything you're taking is actually going to do anything," Cimperman told ABC News. "At the very least, you might be wasting money. At the worst, you might be taking something potentially dangerous."

What's the danger?

"A lot of people might think, 'Oh, it's not a big deal,'" Cimperman said of people taking supplements, adding that patients can't even remember everything they're taking. "It's a false sense of safety and security thinking these things are completely innocuous, they're just vitamins. Anything in very, very high doses or if it's been adulterated can have negative outcomes."

Some patients can have severe allergic reactions to undeclared allergens, but that's not the only thing to worry about, Cimperman said. She pointed to the case of a weight-loss supplement that sent people to the hospital with liver failure in recent years. Some needed liver transplants as a result, she said.

"It's certainly true as well that not all of them are bad and adulterated," Cimperman said. "But wading through and sorting out the good from the bad is difficult."

What should you do?

First, Cimperman said it's crucial to keep your doctor in the loop regarding supplements you're taking. Even if they're perfectly labeled, they can react with your prescription medications. For instance, vitamin K cancels out the effects of some blood thinners, she said.

She said to look for labels that say USP, for U.S. Pharmacopoeia, which independently tests and certify dietary supplements, she said. The four store brands in the the New York attorney general's investigation do not carry this seal.

"We really need to be informed consumers," Cimperman said. "We need to do some digging before we actively start taking these supplements. You really need to involve the doctor in the conversation."