Ginkgo “causes cancer” scare?

Posted by on May 7, 2013 in Uncategorized

In March this year  a NIH Toxicology report on Ginkgo biloba was published,  summarizing the results of a 2 year rodent study on the toxicology of Ginkgo. The  report went largely unnoticed, although a couple of “Consumer Information” sites picked up the summary and issued a “warning” about Ginkgo consumption being associated with cancer. Since then one or two patients have discovered those second hand reports and asked me about the findings and whether there is cause for concern. As a result I have reviewed the full text of the NIH paper. The American Botanical Council has  also issued a critical review of the report.

Toxicological experiments vary widely in their relevance and  applicability of their data to human use. Generally we get better data from long term “pharmacovigilence” studies based on actual historical  use of drugs (or supplements) and cumulative reports of adverse effects or problems. This is relevant in the case of Ginkgo, because since the launch of standardized Gingko extracts (EGb 761) in the late 60’s, many many millions of doses have been taken in Europe and N. America, and the herb has an impressive safety record. Carcinogenesis has never been raised as an issue, and indeed, the herb has numerous anti-cancer properties.

There are several problems with the NIH study. In summary…

1. The extract used was NOT standardized 24/6 Ginkgo (EGb 761) as sold ibn commerce here, but a Chinese extract  which contained higher levels of the toxic ginkgolic acid than permitted by regulations in the US and UK.

2. The doses used were between 25x and 250 x higher than those used in human supplementation. The high dose was 1000mg/Kg which would be the equivalent to  a human dose of 60 GRAMS of extract daily ( the actual human dose is between 120mg-240mg) This would be like taking 750 capsules of 80mg ( the usual dose per cap) daily!

3. Administration was by gastric lavage. In other words a tube was inserted through the animal’s nose into their stomach to apply the “dose” of ginkgo.

4. The ginkgo extract was dissolved in “corn oil”. The provenance of the corn oil was not established. The controls did not receive “placebo oil”.

5. The period of administration was two years! One month for a rodent is considered to be equivalent to 2.5 human years. In other words the excessive doses were applied for the equivalent of 6o human years.

6. Rats ( especially rats!) tend to develop tumors. I have kept pet rats, and back in the day I maintained large research populations of rats and mice, and all sorts of tumors are incredibly common in these animals. The interesting thing in the study was that ONLY thyroid and liver tumors seemed to be increased in the ginkgo group of animals.  Other tumors were the same or LESS than controls. This was never discussed in the sensational summaries of the report. However the implications of that finding remain unclear, especially given the issues with dose etc outlined above.

In general, this study is to all intents and purposes utterly irrelevant with regard to real world ginkgo use by humans. There is simply no reason based on its findings to avoid taking standardized Ginkgo, when indicated or prescribed for appropriate conditions, at the established dose levels (120-240mg daily).


National Toxicology Program. NTP Technical Report on the Toxicology and Carcinogenesis Studies onGinkgo Biloba Extract (CAS NO. 90045-36-6)
 IN F344/N Rats and B6C3F1/N Mice. (Gavage Studies). March 2013. Available at: