Maybe they just forgot to add the gingko biloba.

The New York Attorney General has ordered WalMart (WMT), GNC (GNC), Target (TGT) and Walgreens (WBA) to stop selling certain herbal supplements that it says don't contain the herbal ingredient on the label, or contain only a small amount of it.

The demands came in cease and desist letters addressed to company executives that were dated Monday. The New York Times first reported the letters.

The letters included statements like: "No St. John's Wort DNA was identified." "No plant genetic material of any sort was identified in the product labeled Echinacea." And some contained allergens like wheat that were not properly labeled.

The tests were performed on samples of gingko biloba, St. John's Wort, ginseng, garlic, echinacea and saw palmetto supplements bought from stores in New York. Purchases were made from several stores and samples from each bottle were tested multiple times, according to the attorney general.

The cease and desist order applies only to specific lots of the supplements. But the letters also requested information about the manufacturers and testing procedures to support its "ongoing investigation of this matter."

That investigation is "focused on what appears to be the practice of substituting contaminants and fillers in the place of authentic product," the attorney general's office said.

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"It is our expectation that all suppliers conduct their business and produce products that are in full compliance with the law," WalMart spokesman Brian Nick said. "Based on this notice, we are immediately reaching out to the suppliers of these products to learn more information and will take appropriate action."

Target said it had not yet seen the full report but "is committed to providing high quality and safe products to our guests."

GNC disputed the accuracy of the testing process but said it would comply with the attorney general's order to remove the products from New York shelves.

"We stand behind the quality, purity and potency of all ingredients listed on the labels of our private label products," said Laura Brophy, a spokeswoman for GNC. "GNC tests all of its products using validated and widely used testing methods."

Walgreens said it is removing the products from its shelves and takes the matter "very seriously."

Regulators have long cast a skeptical eye towards herbal supplements, questioning the benefits they promise, but they're subject to much less scrutiny than prescription and over-the-counter drugs.