Widely used around the world to improve mental performance, for circulatory issues, and for vertigo and tinnitus, Ginkgo biloba (leaf extract) dietary supplements have been consistently among the 25 top-selling herbal supplements in the U.S., with over $33 million in sales in 2020 in the natural and mass-market channels combined, according to HerbalGram reporting.

However, over the last two decades, at least 27 publications in peer-reviewed journals have documented cases of adulteration of ginkgo leaf extract ingredients and finished consumer products.

Reviewing various analytical methods used to differentiate between authentic ginkgo leaf extracts and ingredients containing adulterating materials, the ABC-AHP-NCNPR Botanical Adulterants Prevention Program (BAPP) has published a new Laboratory Guidance Document (LGD) on ginkgo (Ginkgo biloba) leaf extracts. This is the 13th publication in the series of LGDs and the 73rd peer-reviewed publication from BAPP.

According to the document, adulteration of ginkgo leaf extracts generally involves the addition of undeclared flavonol-rich ingredients or highly purified flavonoids (e.g., quercetin or rutin) from lower-cost sources, most commonly extracts or purified fractions of the flowers and leaves of Japanese sophora (Styphnolobium japonicum, syn. Sophora japonica).

Of 501 samples analyzed in the 27 papers referenced, 242 (48%) were considered to be adulterated according to criteria established by the authors of each of these publications, suggesting that ginkgo leaf extract adulteration is widespread.

Undeclared added materials typically are rich in rutin and/or quercetin in order to increase the extract content of flavonol glycosides to 24%, the minimum amount specified on the labels of most commercial dietary supplements to meet the same standardization requirement as the extract EGb761 (Dr. Willmar Schwabe GmbH & Co. KG, Karlsruhe, Germany)—the pioneering and most clinically tested ginkgo leaf extract in the world.

Since both rutin and quercetin are also found in ginkgo leaves, the detection of adulteration of commercial ginkgo materials can be challenging.

The new lab guidance document assesses 78 laboratory analytical methods to authenticate ginkgo leaf extract and/or detect ginkgo leaf extract adulteration. The document was compiled and written by Stefan Gafner, PhD, chief science officer of the American Botanical Council (ABC) and technical director of BAPP. It was peer reviewed by 30 experts from academia, government, and the herbal dietary supplement industry.

“Finding a suitable analytical method to authenticate ginkgo leaf extracts is time-consuming at least in part because of the large number of methods available in the peer-reviewed literature, national pharmacopeias, and other official compendia,” said Gafner. “Not many botanical ingredients have been subject to such a vast body of analytical work dedicated to its quality control. We hope that this is where the ginkgo laboratory guidance document can be of value to the international medicinal plant community since it provides an overview of relevant, reliable, and fit-for-purpose methods in a single document.”

Mark Blumenthal, founder and executive director of ABC and founder and director of BAPP, noted: “Standardized ginkgo leaf extract is one of the most clinically researched phytomedicinal products in the world. Many consumers purchase ginkgo products and are sometimes recommended to use them by their health care practitioner in the hope that these products will deliver a clinically documented health benefit. However, if the product contains an intentionally adulterated extract, it is not likely that it will produce the health benefits observed in published clinical trials. Adulteration of ginkgo, or of any herb product, is a great disservice to the millions of people who wish to improve or maintain their health naturally.”

The ABC-AHP (American Herbal Pharmacopoeia)-NCNPR (National Center for Natural Products Research at the University of Mississippi) Botanical Adulterants Prevention Program is an international consortium of nonprofit professional organizations, analytical laboratories, research centers, industry trade associations, industry members, and other parties with interest in herbs and medicinal plants. The program advises industry, researchers, health professionals, government agencies, the media, and the public about various challenges related to adulterated botanical ingredients sold in commerce.