Ginkgo biloba for ADHD?

Guest post by Jan Oude-Aost

ADHD is a common disorder among children. There are evidence based pharmacological treatments, the best known being methylphenidate (MPH). MPH has kind of a bad reputation, but is effective and reasonably safe. The market is also full of alternative treatments, pharmacological and others, some of them under investigation, some unproven and many disproven. So I was not surprised to find a study about Ginkgo biloba as a treatment for ADHD. I was surprised, however, to find this study in the German Journal of Child and Adolescent Psychiatry and Psychotherapy, officially published by the “German Society of Child and Adolescent Psychiatry and Psychotherapy“ (Deutsche Gesellschaft für Kinder- und Jugendpsychiatrie und Psychotherapie). The journal’s guidelines state that studies should provide new scientific results.

The study is called “Ginkgo biloba Extract EGb 761® in Children with ADHD“. EGb 761® is the key ingredient in “Tebonin®“, a herbal drug made by “Dr. Wilma Schwabe GmbH“. The abstract states:

“One possible treatment, at least for cognitive problems, might be the administration of Ginkgo biloba, though evidence is rare.This study tests the clinical efficacy of a Ginkgo biloba special extract (EGb 761®) (…) in children with ADHD (…).“

“Eine erfolgversprechende, bislang kaum untersuchte Möglichkeit zur Behandlung kognitiver Aspekte ist die Gabe von Ginkgo biloba. Ziel der vorliegenden Studie war die Prüfung klinischer Wirksamkeit (…) von Ginkgo biloba-Extrakt Egb 761® bei Kindern mit ADHS.“ (Taken from the English and German abstracts.)

The study sample (20!) was recruited among children who “did not tolerate or were unwilling“ to take MPH. The unwilling part struck me as problematic. There is likely a strong selection bias towards parents who are unwilling to give their children MPH. I guess it is not the children who are unwilling to take MPH, but the parents who are unwilling to administer it. At least some of these parents might be biased against MPH and might already favor CAMmodalities.

The authors state three main problems with “herbal therapy“ that require more empirical evidence: First of all the question of adverse reactions, which they claim occur in about 1% of cases with “some CAMs“ (mind you, not “herbal therapy“). Secondly, the question of drug interactions and thirdly, the lack of information physicians have about the CAMs their patients use.

A large part of the study is based on results of an EEG-protocol, which I choose to ignore, because the clinical results are too weak to give the EEG findings any clinical relevance.

Before looking at the study itself, let’s look at what is known about Ginkgo biloba as a drug. Ginkgo is best known for its use in patients with dementia, cognitive impairment und tinnitus. A Cochrane review from 2009 concluded:

“There is no convincing evidence that Ginkgo biloba is efficacious for dementia and cognitive impairment“ [1].

The authors of the current Study cite Sarris et al. (2011), a systematic review of complementary treatment of ADHD. Sarris et al. mention Salehi et al. (2010) who tested Ginkgo against MPH. MPH turned out to be much more effective than Ginkgo, but Sarris et al. argue that the duration of treatment (6 weeks) might have been too short to see the full effects of Ginkgo.

Given the above information it is unclear why Ginkgo is judged a “possible“ treatment, properly translated from German even “promising”, and why the authors state that Ginkgo has been “barely studied“.

In an unblinded, uncontrolled study with a sample likely to be biased toward the tested intervention, anything other than a positive result would be odd. In the treatment of autism there are several examples of implausible treatments that worked as long as parents knew that their children were getting the treatment, but didn’t after proper blinding (e.g. secretin).

This study’s aim was to test clinical efficacy, but the conclusion begins with how well tolerated Ginkgo was. The efficacy is mentioned subsequently: “Following administration, interrelated improvements on behavioral ratings of ADHD symptoms (…) were detected (…).“ But the way they where “detected“ is interesting. The authors used an established questionnaire (FBB-HKS) to let parents rate their children. Only the parents. The children and their teachers where not given the FBB-HKS-questionnaires, inspite of this being standard clinical practice (and inspite of giving children questionnaires to determine changes in quality of life, which were not found).

None of the three problems that the authors describe as important (adverse reactions, drug interactions, lack of information) can be answered by this study. I am no expert in statistics but it seems unlikely to me to meaningfully determine adverse effects in just 20 patients especially when adverse effects occur at a rate of 1%. The authors claim they found an incidence rate of 0,004% in “700 observation days“. Well, if they say so.

The authors conclude:

“Taken together, the current study provides some preliminary evidence that Ginkgo biloba Egb 761® seems to be well tolerated in the short term and may be a clinically useful treatment for children with ADHD. Double-blind randomized trials are required to clarify the value of the presented data.“

Given the available information mentioned earlier, one could have started with that conclusion and conducted a double blind RCT in the first place!

“Clinical Significance

The trends of this preliminary open study may suggest that Ginkgo biloba Egb 761® might be considered as a complementary or alternative medicine for treating children with ADHD.“

So, why do I care? If preliminary evidence “may suggest“ that something “might be considered“ as a treatment? Because I think that this study does not answer any important questions or give us any new or useful knowledge. Following the journal’s guidelines, it should therefore not have been published. I also think it is an example of bad science. Bad not just because of the lack of critical thinking. It also adds to the misinformation about possible ADHD treatments spreading through the internet. The study was published in September. In November I found a website citing the study and calling it “clinical proof“ when it is not. But child psychiatrists will have to explain that to many parents, instead of talking about their children’s health.

I somehow got the impression that this study was more about marketing than about science. I wonder if Schwabe will help finance the necessary double-blind randomized trial…