Many of the herbal supplements found on store shelves may not contain the ingredients listed on their labels, a recent investigation of several store-brand-name products in New York has revealed. The research supports a growing body of evidence that the majority of the products available have been adulterated with elements or fillers not included in their descriptions.

Four retailers in New York agreed Thursday to pull certain dietary supplements from their stores after the state’s attorney general, Eric Schneiderman, threatened legal action for selling products found to be bogus. Earlier DNA tests of the supplements detected none of the plant materials listed on most of the products’ bottles, according to Reuters. Investigators tested dietary supplements from four major retailers – GNC, Target, Walgreens and Walmart – and found that only 21 percent of the samples showed traces of the herbs they claimed to contain.

“This investigation makes one thing abundantly clear: the old adage ‘buyer beware’ may be especially true for consumers of herbal supplements,” Schneiderman said in a statement earlier this month. "The DNA test results seem to confirm long-standing questions about the herbal supplement industry. … At the end of the day, American corporations must step up to the plate and ensure that their customers are getting what they pay for, especially when it involves promises of good health.”

The products tested were Echinacia, which has been used to fight infections; garlic; gingko biloba, which is often taken for memory disorders; ginseng; saw palmetto, which is used to treat prostate issues; and St. John’s wort, taken for depression or anxiety.

The multivitamin, minerals and herbs industry is a multi-billion-dollar trade, however research has shown that many of the products out there are not what they claim to be. A 2013 study of 44 popular products found that more than one-third of them did not contain the ingredients listed. Herbal supplements that promised to enhance memory, boost mood or fight colds were mostly a sham. Many contained little other than “alternative plant species and fillers” like powdered rice, researchers noted in the study published in the journal BMC Medicine.

Manufacturers of herbal supplements are not required to seek approval from the Food and Drug Administration in the same way that drug manufacturers are compelled to, and their products are not analyzed by the FDA before they are sold to consumers.

On its website, the FDA details how it handles oversight of dietary supplements. “In that FDA has limited resources to analyze the composition of food products, including dietary supplements, it focuses these resources first on public health emergencies and products that may have caused injury or illness,” the agency said