NEW YORK — The New York Attorney General’s Office has sent letters to four manufacturers of dietary supplements requesting information on the ingredients and quality control measures used for their products sold in the state.

New York Attorney General Eric Schneiderman sent the letters this week to Pharmavite LLC, Nature’s Way Products Inc., NBTY Inc. and Nutraceutical Corp., explaining that the information request stems from his office’s ongoing probe into the authenticity, purity and marketing of herbal dietary supplements.

Earlier this month, Schneiderman sent cease-and-desist letters to Walgreens, Walmart, Target and GNC asking the retailers to stop selling certain store-brand herbal supplements because DNA testing revealed discrepancies with ingredients listed on their labels.

“The scientific community, public health officials and others have raised serious doubt about the steps taken to ensure the safety and efficacy of the herbal dietary supplements taken daily by millions of Americans. As part of a broader investigation, NYAG is reviewing the sufficiency of the measures manufacturers and retailers are taking to independently assess the validity of their representations and advertising in connection with the sale of herbal supplements. We seek your company’s cooperation as an herbal dietary supplement manufacturer to address these issues and, ultimately, to resolve any deficiencies,” Schneiderman’s letters to Pharmavite, Nature’s Way, NBTY and Nutraceutical Corp. said.

“As you may know, NYAG recently commissioned an analysis that used DNA barcoding technology to test several popular herbal dietary supplements sold at four retailers in New York state. The results were shocking to many consumers and raise troubling legal questions. In addition to the frequent absence of genetic material associated with the plant depicted on the label from the tested supplements, more than one in three samples tested positive for the DNA of an unlisted plant species, potentially constituting a contaminated or substituted product.”

The Feb. 23 letters to the manufacturers seek such information as the names and brands of the herbal dietary supplement products they sell in New York and the analytic testing used “to confirm the content, quality, purity or chemical composition” of ingredients, components or fillers as well as the finished products.

Other information requested in the letters includes a description of quality control measures taken across the supply chain for the manufacturers’ herbal dietary supplements, “including but not limited to the implementation of Good Farming and Collection Practices (GACPs) or Current Good Manufacturing Practices (CGMPs),” as well as a description of testing performed on finished products to substantiate claims such as “gluten-free” or “hypoallergenic.”

“Attorney General Schneiderman is committed to ensuring that the roughly 150 million Americans who use herbal supplements know what is in the products they are consuming,” New York Attorney General’s Office spokesman Matt Mittenthal said in a statement. “It’s important for both retailers and manufacturers to verify the contents of the products they sell so consumers can be protected against deceptive claims on packaging and against potentially dangerous reactions to undisclosed ingredients.”

Mission Hills, Calif.-based Pharmavite is the maker of the Nature Made supplements brand. The roster of brands from Ronkonkoma, N.Y.-based NBTY includes Nature’s Bounty and Sundown Naturals, among others. Nature’s Way Products, which has its headquarters in Lehi, Utah, makes the Nature’s Way supplements brand, while Park City, Utah-based Nutraceutical Corp. offers a range of brands such as Solaray, Nature’s Life, Natural Balance and Herbs for Kids, among others.

The store brands at issue in the New York attorney general’s investigation are GNC’s Herbal Plus, Walgreens’ Finest Nutrition, Walmart’s Spring Valley and Target’s Up & Up.

In its analysis of the store-brand supplements — gingko biloba, St. John’s wort, ginseng, garlic, echinacea and saw palmetto — the attorney general’s office found that, overall, 21% of the test results verified DNA from the plants listed on the products’ labels, with 79% coming up empty for DNA related to the labeled content or verifying contamination with other plant material. Also, 35% of the product tests identified DNA barcodes from plant species not listed on the labels

Supplement industry stakeholders have blasted the investigation, namely its reliance on DNA barcode testing, which they called an unreliable and limited method for testing the identity of herbal dietary supplements.

On Tuesday, in response to the letters to the supplement manufacturers, Natural Products Association (NPA) chief executive officer and executive director Daniel Fabricant criticized Schneiderman for not sharing the data from his office’s analysis of the store-brand supplements.

“It’s been three weeks since the attorney general asked retailers to remove products from their shelves without sharing the study data that served as the scientific basis for this request. The Natural Products Association has serious concerns over the scientific basis for that recall,” Fabricant said in a statement. “It has been more than a week since the winds of change from the attorney general focused attention away from DNA in botanical extracts and toward structure/function claims for ingredients with established science behind them. These actions set a dangerous precedent not just for dietary supplement retailers but for the entire retail market, including manufacturers and ingredient suppliers.”

Fabricant also claimed that Schneiderman’s probe goes beyond the scope of his office.

“All of the information the attorney general is requesting from these manufacturers can be accessed by the Food and Drug Administration. The federal government is fully equipped to regulate dietary supplements and goes to great lengths to ensure consumer and public health is protected. If the FDA finds issues with manufacturers, it swiftly and resolutely takes action against those firms. In my time at the agency, we were not shy about going after those who put consumers are risk,” stated Fabricant, a former director of the dietary supplement programs division at the Food and Drug Administration. “It is perplexing as to why Attorney General Schneiderman continues to use resources to address dietary supplement matters, which do not fall within his authority and are already handled by the regulators within the federal government.”

Supplement makers have stood by their products and their manufacturing and quality control standards.

Earlier this month, NBTY announced the formation of a scientific advisory council of medical and nutrition experts to provide insight into nutrition and health trends, assist the company in advancing its global scientific efforts, and offer guidance on product development and innovation.

“Maintaining our high-quality standards, whether we are talking about the ingredients, the manufacturing processes or the scientific data that supports each of our products, is of the utmost importance to us,” stated Dr. Susan Hazels Mitmesser, director of nutrition research at NBTY and a member of the council. “We are honored to have the expertise of this council available to us.”