THE BLOG

Is Ginkgo Dangerous?

05/18/2013 09:58 am ET | Updated Jul 18, 2013
  • Dr. Andrew Weil Founder and director, The Arizona Center for Integrative Medicine
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Many people have expressed concern to me following recent news stories about a government report on the safety of ginkgo biloba extract.

I view the stories about this study as misleading. The worrisome conclusion that the public seems to be drawing from them is that a government agency has shown that ginkgo extract supplements raise the risk of cancer in human beings.

That conclusion is absolutely incorrect. I'd like to discuss it not only to illuminate this particular case, but to provide the reader with some perspective to help analyze stories like these as they arise. They are all too common, I'm afraid.

The report in question is from the National Toxicology Program (NTP), a federal interagency group charged with providing information about potentially toxic substances to government, private entities and the public. It bears the daunting title "NTP Technical Report on the Toxicology and Carcinogenesis Studies of Ginkgo Biloba Extract (CAS No. 90045 - 36 - 6) in F344/N Rats and B6C3F1/N Mice (Gavage Studies)." At 184 pages, it's a dense read -- far too much for the average reporter under deadline to fully comprehend and condense.

That's unfortunate, because while the rats and mice did develop cancers at high rates over the two-year course of study, there are at least two important ways in which the rodents' experience differed dramatically from that of human beings taking ginkgo supplements. These were raised by the American Botanical Council (ABC) in public comments it sent to the NTP:

  • The extract used was manufactured by a specific Chinese company and is "not consistent with" the standards for quality set forth in official profiles used by prominent botanical medicine testing agencies, particularly those in Europe. This means that the results "are not applicable to the standard-setting ginkgo extracts," the ABC said.
  • Adjusted for bodyweight, dosage levels given to the animals were up to 55 to 108 times higher than levels of ginkgo normally ingested by human beings taking ginkgo supplements.

"Almost anything will create cancer in rats and mice when it's fed to them at high doses for two years," commented Bill J. Gurley, Ph.D., professor of pharmaceutical sciences in the College of Pharmacy at the University of Arkansas School for Medical Sciences, Little Rock.

"At best, what NTP can say is that significantly high doses of this particular Shanghai Chinese ginkgo extract -- when added to a corn-oil base -- produced cancer in the lab animals," added Mark Blumenthal, ABC's executive director.

To this, I would add my own observation based on over 40 years of research into both synthetic pharmaceuticals and botanical medicines.

Synthetic pharmaceuticals, generally speaking, should be regarded as guilty until proven innocent. This is because they often represent novel molecules and compounds with which human beings have no evolutionary experience. Synthesizing chemicals and expecting them to integrate harmlessly -- even helpfully -- into the complex biochemistry of human metabolism is often an act of unwarranted hubris. From Thalidomide to Vioxx to Meridia, over and over again we've discovered that there are unintended consequences to presenting the human body with chemical creations it has never encountered before. This is not to say all pharmaceuticals are dangerous, only that they should be given high evidentiary hurdles to clear before they are declared safe.

Conversely, a botanical medicine with which human beings have long, positive associations should be seen as innocent until proven guilty. The fact that cultures around the world have used, embraced and developed guidelines around the use of a given herbal medicine is important. It suggests that over hundreds or thousands of years, large groups of human beings (as opposed to rodents) using the medicine in moderate dosages (as opposed to megadoses) have found it safe and useful.

Modern research can refine that knowledge. But I am hard pressed to understand how massively overdosing rodents with an odd, non-representative version of a botanical medicine assists in that effort.

Based on this study, if you take high-quality ginkgo extract in typical dosages -- I recommend 120 mg daily in divided dosages, taken with food -- and have enjoyed good results, I see no reason to discontinue that use. Beyond that, I look forward to rigorous studies based on human consumption at appropriate levels of high-quality botanical medicines. These can help us make even better use of the healing potential of these natural substances, as well as to make us aware of any potential risks.

Andrew Weil, M.D., is the founder and director of the Arizona Center for Integrative Medicine and the editorial director of www.DrWeil.com. Become a fan on Facebook, follow Dr. Weil on Twitter, and check out his Daily Health Tips Blog.

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