Product Review: Ginkgo Biloba and Huperzine A — Memory Enhancers
Initial Posting: 4/21/03

What It Is:
Ginkgo biloba in dietary supplements is typically an extract made from leaves of the Ginkgo biloba tree and containing many phytochemicals. Huperzine A, in dietary supplements, is a chemical purified from leaves of the Chinese toothed club moss (Huperzia serrata (Thunb. ex Murray) Trevis) or synthetically manufactured.

What It Does:
Ginkgo biloba:
Ginkgo biloba has become a widely used dietary supplement for increasing cognitive functions in elderly people, delaying the progression of Alzheimer's disease, increasing blood flow to the legs, treating tinnitus (ringing in the ear) of a circulatory origin, as well as treating depression and asthma.

Huperzine A:
Huperzine A, based on limited studies, has been shown to improve memory, thinking, and behavioral function in people with Alzheimer's disease, multi-infarct dementia, and senile dementia.. It is believed to work in a manner similar to some prescription drugs for treating symptoms of Alzheimer's disease: increasing the level of the neurotransmitter acetylcholine by blocking its breakdown. It may also protect neurons from cell death caused by toxic levels of glutamate and protect against some of the effects of chemical nerve agents used in warfare, such as soman.

Quality Concerns and What CL Tested for:
Ginkgo Biloba:
The Ginkgo biloba extract, or GBE, used in most clinical trials contains particular phytochemicals: Flavonol glycosides, of which there are three basic types, are believed to confer anti-oxidant activity; Terpene lactones, of which there are two basic types, may be responsible for the dilatory effect on blood vessels. One specific terpene lactone called bilobalide, may also increase brain activity through an effect on GABA receptors. Specifically, the GBE shown to work in clinical trials has contained at least 5% terpene lactones (consisting of bilobalide (2.6%) and ginkgolides A, B and C (2.8%)) and at least 22% flavonol glycosides (consisting of quercetin (9.5%), kaempferol (10.5%), and isorhamnetin (2.0%).

Many GBE products now claim to be "standardized" or manufactured to contain specific total amounts of flavonol glycosides and/or total terpene lactones, but few claim to have specific amounts of the individual compounds, such as bilobalide. However, ConsumerLab.com's review of GBE products in 1999 found that nearly one quarter of the thirty brands tested did not have the expected levels of chemical marker compounds for GBE, despite claims to have been "standardized."

Huperzine A:
Only the (-) isomer of huperzine A is active. However, if a product is made from synthetic huperzine A, at least 50% of its huperzine A will be inactive, and often products do not state the form of huperzine A that they contain. The labeled amount of huperzine A of a product should reflect only the active form. Huperzine A is also a relatively expensive ingredient, creating an economic incentive for making a product with less than the labeled amount.

Lead in Natural Products:
Lead is a potential contaminant in natural products. In children, infants, and fetuses, even low levels of lead can adversely affect neurobehavioral development and cognitive function. In adults, lead at somewhat higher levels can cause elevated blood pressure, anemia, and adversely affect the nervous and reproductive systems. Lead is of particular concern during pregnancy as the mother can transfer it to the fetus.

Currently, there is no government monitoring of the manufacture of dietary supplements in the U.S. In order to help consumers identify products of better quality, ConsumerLab.com purchased and tested many Ginkgo biloba and huperzine A products and tested them for the quality of their ingredients and lead levels. In addition, products in tablet form were tested for their ability to properly disintegrate in solution — which is necessary for their ingredients to be absorbed.

What CL Found
ConsumerLab.com purchased nine brands of Ginkgo biloba and four brands of huperzine A in December 2002 and January 2003  In testing, seven of the nine ginkgo products were found to lack adequate levels of one or more important compounds expected of clinically effective ginkgo. Many of these products claimed to be standardized for total terpene lactones and/or flavonol glycosides and did, in fact, meet these totals but did not have the right amount of one or more individual terpene lactones and flavonol glycosides. In fact, 6 products had less than one-fifth of the expected amount of bilobalide, a type of terpene lactone that may be particularly important to ginkgo's effectiveness. Bilobalide has specifically been shown to interact with GABA receptors and enhance the excitability of neurons in the hippocampus of the brain, which is associated with learning and memory.

All of the huperzine A products were found to contain their claimed amount of huperzine A in the active (-) isomer form. However, one product contained an unacceptable amount of lead.

All products in tablet form were found to disintegrate properly in solution, as needed for absorption in the gut.

Test Results by Product:
Listed alphabetically in the table below are the products that were tested and a summary of their results. Products that met all of ConsumerLab.com's Passing Score criteria are indicated as "Approved Quality" and are listed first in their category. Also included in the list are other products that have met the same criteria through CL's Voluntary Certification Program (these are indicated with an asterisk).