Ginkgo biloba leaf extract is the most thoroughly tested cognitive supplement. The definitive test — the NIH-funded GEM trial, 3,069 older adults taking 240 mg/day of standardized extract for a median six years — found no reduction in dementia, Alzheimer's, or the rate of cognitive decline versus placebo. Trials in people who already have dementia are mixed: modest benefit in European studies of the EGb 761 extract, none in comparable US trials. It does not enhance memory in healthy adults. Small effects exist for leg-artery circulation. Ginkgo is generally tolerated but inhibits platelets — a real interaction with blood thinners and surgery.
What ginkgo is
Ginkgo biloba is a living fossil — the last species of a tree lineage older than dinosaurs — whose fan-shaped leaves yield the extract that became, for decades, the world's best-selling memory supplement. Standard products are 50:1 leaf extracts standardized to 24% flavone glycosides and 6% terpene lactones (the specification of EGb 761, the extract most trials used), dosed at 120–240 mg per day.
Its proposed mechanisms are respectable: improved microcirculation, antioxidant activity, platelet-activating-factor inhibition, and effects on neurotransmitters. The question was always whether any of it moved human outcomes. Unusually, we found out.
Evidence by use
Preventing dementia and cognitive decline — the definitive answer. The GEM trial (Ginkgo Evaluation of Memory) was built to settle the marquee claim: 3,069 community-dwelling adults aged 72–96, randomized to 240 mg/day of standardized extract or placebo, followed for a median 6.1 years. Result: no reduction in all-cause dementia or Alzheimer's disease, and no slowing of decline on any cognitive domain in the companion analysis. A comparable French trial (GuidAge, 2,854 adults, five years) also found no reduction in Alzheimer's. For the prevention claim that sold most of the bottles, the evidence is about as negative as trial evidence gets.
Treating existing dementia. Genuinely mixed. Several European trials of EGb 761 at 240 mg/day in mild-to-moderate dementia — particularly with neuropsychiatric symptoms — reported modest improvements in cognition, function and behavior; well-run US trials found no benefit. Meta-analyses lean cautiously positive for that specific extract at that dose, with heterogeneity nobody has fully explained. In practice: a conversation for the physician managing a diagnosed dementia, not a self-directed purchase.
Memory in healthy adults. Trials in younger and older healthy volunteers show no consistent enhancement of memory or attention — the honest reading of a literature the marketing ignores. Wider aisle context: Do memory supplements work?
Circulation (intermittent claudication). Meta-analyses find small increases in pain-free walking distance in leg arterial disease — real, modest, and inferior to supervised exercise therapy.
Tinnitus, vertigo, altitude sickness, sexual dysfunction from antidepressants. Reviews land negative-to-inconclusive; the tinnitus literature is negative overall with a possible signal in dementia populations.
Doses studied
120–240 mg/day of the standardized 24/6 extract, in two or three doses; dementia trials used 240 mg. Effects, where trials found any, took weeks. Teas and unstandardized leaf products are not equivalent to the trialled article.
Safety
Well tolerated at trial doses: headache, stomach upset, dizziness and palpitations occur at placebo-adjacent rates. The concerns that matter:
- Bleeding. Platelet inhibition plus case reports of serious bleeds — nearly always alongside warfarin, DOACs, aspirin, clopidogrel or NSAIDs. Anticoagulated patients should not add ginkgo without prescriber sign-off, and everyone should stop it two weeks before surgery.
- Seizure threshold — case reports of seizures; caution in epilepsy, and avoid the toxic raw seeds entirely.
- Drug interactions beyond bleeding: possible effects on some antidepressants, anticonvulsants and diabetes medication metabolism — pharmacist territory.
- Pregnancy — avoid (bleeding concern around delivery).
- A US National Toxicology Program study found liver tumors in rodents at high extract doses; human relevance is debated, but it is another argument against megadosing.
Where it appears in supplements
As a stand-alone and in nearly every "memory," "focus" and "brain" blend — typically 30–120 mg of unspecified extract, below the trialled dose, alongside a crowd of other ingredients. The blend format inherits ginkgo's interactions while abandoning its dosing. See brain supplement research.
Bottom line
Ginkgo earned a definitive test and, for prevention and healthy-adult enhancement, failed it — which spares your money. The residual live questions (EGb 761 in diagnosed dementia, claudication) belong in a doctor's hands because that is where the conditions belong. For the worried-well brain, the interventions with actual evidence are unglamorous: sleep, exercise, hearing aids where needed, blood pressure control, and staying engaged — the case laid out in Do memory supplements work?
Frequently asked questions
What exactly did the GEM trial test?
Ginkgo Evaluation of Memory randomized 3,069 adults aged 72–96 (normal cognition or mild impairment) to 120 mg twice daily of standardized extract or placebo, followed for a median 6.1 years. Dementia occurred at the same rate in both groups, cognitive decline proceeded at the same rate, and cardiovascular events did not differ. It remains the largest and longest supplement trial for dementia prevention.
Why do European guidelines mention ginkgo for dementia if US trials failed?
The positive trials cluster around one standardized extract (EGb 761) tested in European populations with dementia plus behavioral symptoms, where modest improvements in cognition and daily function appeared. US trials with similar designs found nothing. Reviewers split on whether extract, populations or chance explains it — hence "mixed," and hence at best a discussion with a doctor in diagnosed dementia, not self-treatment.
Is ginkgo dangerous with aspirin or warfarin?
The combination raises bleeding concern enough that case reports and pharmacology both say tell your prescriber. Ginkgo inhibits platelet-activating factor; spontaneous bleeds have been reported, mostly with anticoagulants or antiplatelets aboard. It is also standard advice to stop ginkgo two weeks before surgery or dental extraction.
Are ginkgo seeds edible?
Raw or undercooked seeds are toxic — they contain ginkgotoxin, which can cause seizures, and have poisoned children in seed-eating regions. Supplements use leaf extract; the seed issue is a food-safety note, not a supplement one.
References
- NCCIH. Ginkgo (2020). https://www.nccih.nih.gov/health/ginkgo
- National Institute on Aging. Memory Problems, Forgetfulness, and Aging (2023). https://www.nia.nih.gov/health/memory-loss-and-forgetfulness/memory-problems-forgetfulness-and-aging
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