* The herbal supplement ginkgo is popular worldwide as a memory-enhancing agent.
* Clinical data, not yet definitive, suggest that standardized extracts can be beneficial in dementia.
History and Rationale for Use
Extracts of the seeds, leaves, and fruit of the Ginkgo biloba tree have been used in Chinese medicine for more than 5,000 years for age-related maladies, asthma, and parasitic diseases such as filariasis.
Ginkgo continues to be a central element of modern Chinese therapy for chronic bronchitis, cardiovascular symptoms, and dyslipidemia.
Ginkgo was first described to the West by Englebert Kaempfer, a German surgeon with the Dutch East India Co. The tree was introduced to North America in 1784, in the gardens at Woodland near Philadelphia (American Botanical Council Series 304, 1996). Ginkgo is one of the best-selling phytomedicines in Germany, where a standardized, pharmaceutical-grade extract (EGb 761, Schwabe) is recommended by Commission E for cognitive and circulatory disorders. It is the top-selling herbal supplement in the United States, with 1998 retail sales of $151 million (Ann. Intern. Med. 136:42-53, 2002).
Ginkgo's therapeutic effects are thought to derive from its ability to prevent oxidative stress and its effects on peripheral and central neurotransmitter systems. Extracts of the plant contain many potentially active constituents including flavonoids, terpenoids, and phenolic acids. These have multiple and apparently synergistic pharmacologic actions, including free-radical scavenging, inhibition of membrane lipid peroxidation, vasodilation, and antihypoxia effects. Ginkgolides in the plant have antiplatelet effects.
Clinical Study Findings
Many studies, primarily done in Germany, have evaluated ginkgo for treating cognitive impairment. A systematic review identified 18 double-blind, randomized, placebo-controlled studies (Clin. Drug. Invest. 17:301-08, 1999). In general, the studies showed that cognitively impaired patients given ginko improved on tests of psychomotor performance. But assessing the quality of the data from some of the studies is problematic. Listed diagnoses included ill-defined entities such as "cerebral insufficiency" and "cerebroorganic syndrome"; it was not dear in many cases if dementia was present.
"They were a heterogeneous group of elderly patients who complained that their memory wasn't as good as it used to be," Dr. Lon S. Schneider told this newspaper.
More recent studies tried to correct the shortcomings of early European studies, which were limited in duration and did not use standardized assessments. The longest study to date was a 1-year randomized, double-blind study of patients with mild to moderately severe dementia of the Alzheimer's or multi-infarct types, at six U.S. research centers.
Patients received 120 mg/day of EGb 761 or placebo. The primary outcome measures were cognitive impairment (the Cognitive Subscale of the Alzheimer's Disease Assessment Scale, or ADAS-Cog), daily living and social behavior (the Geriatric Evaluation by Relative's Rating Instrument), and general psychopathology (the Clinical Global Impression of Change). …