Ginkgo and bleeding risk is a case where two kinds of evidence point in opposite directions, and neither can be dismissed.
Case reports describe serious haemorrhage. Randomised trials measuring coagulation find nothing. Working out what to do with that requires looking at what each kind of study can and cannot detect.
The mechanism is real
Ginkgo contains ginkgolide B, a potent antagonist of platelet-activating factor (PAF)[3].
PAF is a phospholipid that promotes platelet aggregation and inflammation[6]. Blocking it reduces platelets’ ability to stick together and form clots.
That’s not a speculative pathway. It’s a defined pharmacological action with a named compound, and it’s the reason the question arises at all.
What the case reports describe
The published cases are serious.
Reported events range from nosebleeds and ocular bleeding to life-threatening intracranial bleeding[3].
One documented case: a 78-year-old man developed headache, confusion and progressive right-sided weakness following a fall. A large subdural haematoma was found. His only prior medications were lisinopril and ginkgo biloba, 50 mg three times daily[2].
Another report described fatal intracerebral bleeding associated with ginkgo and ibuprofen[3].
A retrospective analysis of a large US Veterans Administration database examined bleeding in patients on warfarin who also took ginkgo. The results were interpreted as suggesting increased risk of bleeding-related adverse events[5].
What the randomised trials found
Now the other side, and it’s substantial.
A meta-analysis of 18 randomised controlled trials enrolling 1,985 adults assessed haemostasis parameters directly[1].
The findings[1]:
- ADP-induced platelet aggregation: no significant effect (WMD −0.35%, 95% CI −15.16 to 14.46)
- Fibrinogen concentration: no significant effect
- aPTT: no significant effect
- Prothrombin time: no significant effect
- Blood viscosity: significantly reduced (WMD −1.03 mPa·sec, 95% CI −1.29 to −0.78)
Only viscosity moved — which is the circulation effect ginkgo is marketed on, not a clotting defect.
Two individual trials point the same way. A randomised trial gave EGb 761 at 300 mg/day alongside 325 mg/day aspirin to older adults with peripheral artery disease or cardiovascular risk. No clinically or statistically significant differences appeared on any measure, and bleeding or bruising reports were infrequent and similar in both groups[4].
And a secondary analysis of an Alzheimer’s trial found that none of 29 coagulation and bleeding parameters showed evidence of EGb 761 inhibiting coagulation or platelet aggregation, with no pharmacodynamic interactions with warfarin or acetylsalicylic acid[5][6].
Reconciling the two
Case reports and trials answer different questions, and that explains most of the divergence.
Case reports capture rare events. A trial of a few hundred people over weeks won’t detect something occurring in one person in tens of thousands. Absence of an event in 1,985 participants doesn’t establish that the event never happens.
Trials capture average effects. A meta-analysis showing no mean change in platelet aggregation is strong evidence that ginkgo doesn’t broadly impair clotting — but says little about an individual with unusual susceptibility.
Case reports can’t establish causation. Establishing direct causality from a case report remains difficult[6]. Someone taking ginkgo who bleeds may have bled anyway.
So the reasonable summary: ginkgo does not appear to impair coagulation in the general case, and rare serious events have been reported that cannot be attributed with confidence.
Where the signal is stronger
One finding sharpens this considerably.
A 2025 comprehensive analysis published in PLOS One found ginkgo drug interactions were significantly associated with bleeding risk (OR 1.08, p < 0.001) and abnormal coagulation — particularly when combined with antiplatelet drugs such as clopidogrel and aspirin[6].
The same analysis noted that the independent bleeding risk of ginkgo without co-medications remains uncertain based on RCT data[6].
Read together with everything above, that’s a coherent picture. The concern isn’t ginkgo alone. It’s ginkgo plus something already affecting platelets or clotting.
Which matches the case reports, several of which involved concomitant warfarin, aspirin or ibuprofen.
Before surgery
Here the recommendation is straightforward despite the evidence being mixed.
The conservative approach, given the case reports of serious bleeding, is to discontinue ginkgo before surgery[6]. Most guidance recommends stopping supplements affecting haemostasis — fish oil, vitamin E and ginkgo among them — 7 to 14 days before surgery[6].
The asymmetry justifies the caution. Stopping a supplement for two weeks costs almost nothing. Intraoperative bleeding is a serious problem. When the downside of caution is negligible and the downside of the alternative isn’t, caution wins regardless of how the evidence balance sits.
Disclose all supplements to your surgeon, not just prescriptions[6]. This is the step most often skipped, because supplements aren’t mentally filed as medicines.
What to do
If you take ginkgo and no other medication, the RCT evidence is reasonably reassuring on coagulation parameters. That isn’t a guarantee, and unusual bleeding or bruising warrants attention rather than dismissal.
If you take an anticoagulant or antiplatelet drug, this is where the signal is. Raise it with the prescriber rather than deciding either way yourself.
If you take NSAIDs regularly, the same applies — one fatal case involved ibuprofen.
If surgery or a dental procedure is scheduled, tell the clinician and expect to stop 7–14 days ahead.
Do not stop a prescribed medication on your own to accommodate a supplement. That inverts the priority entirely.
And a note specific to Korea, from the earlier ginkgo post: ginkgo leaf extract is available here as a medicine as well as a supplement. Someone taking both a prescribed ginkgo product and a ginkgo supplement is doubling a dose without realising it — which is worth checking before anything else.
Closing
I’d carried a vague sense that ginkgo thins the blood, and treated that as settled. The trial data doesn’t support it as a general effect — eighteen trials, nearly two thousand people, and no measurable change in platelet aggregation or clotting times.
What survives is narrower and more specific. A defined mechanism that exists. Rare serious case reports that can’t be attributed with confidence. And an interaction signal that shows up clearly when ginkgo meets a drug already acting on platelets.
That’s a different caution from “ginkgo thins your blood.” It’s closer to: on its own, probably not much; combined with something that does, worth a conversation.
And before surgery, stop it — not because the evidence demands it, but because the cost of stopping is so low that the evidence doesn’t need to.
At a Glance
- Ginkgolide B is a potent platelet-activating factor antagonist — the mechanism is real
- Case reports describe nosebleeds, ocular bleeding, subdural haematoma and fatal intracerebral bleeding
- A meta-analysis of 18 RCTs, 1,985 adults found no significant effect on platelet aggregation, fibrinogen, aPTT or prothrombin time
- Blood viscosity was reduced — a circulation effect, not a clotting defect
- EGb 761 alongside 325 mg/day aspirin produced no detectable change over four weeks
- A secondary analysis found none of 29 coagulation parameters affected, and no interaction with warfarin or aspirin
- A 2025 analysis found ginkgo drug interactions associated with bleeding risk (OR 1.08, p < 0.001), especially with clopidogrel and aspirin
- Independent risk without co-medication remains uncertain; standard advice is to stop 7–14 days before surgery
※ This article is for general information and does not replace medical advice, diagnosis or treatment. Do not start or stop any supplement or medication on your own. If you take anticoagulant or antiplatelet medication, or have any procedure scheduled, disclose all supplements to your clinician. Unusual bruising, bleeding that is slow to stop, or blood in urine or stool warrants prompt medical attention.
References
- Kellermann AJ, Kloft C. “Is there a risk of bleeding associated with standardized Ginkgo biloba extract therapy? A systematic review and meta-analysis”, Pharmacotherapy 2011;31(5):490-502, https://pubmed.ncbi.nlm.nih.gov/21923430/
- “Does Ginkgo biloba increase the risk of bleeding? A systematic review of case reports” (subdural haematoma case; haemorrheological data), https://www.researchgate.net/publication/286867621_Does_Ginkgo_biloba_increase_the_risk_of_bleeding_A_systematic_review_of_case_reports
- “The use of Ginkgo biloba may increase the risk of bleeding”, European Glaucoma Society (ginkgolide B mechanism; range of reported events), https://eugs.org/news/the-use-of-ginkgo-biloba-may-increase-the-risk-of-bleeding-2013-05-31-tip-of-the-month
- “Effect of Ginkgo biloba (EGb 761) and aspirin on platelet aggregation and platelet function analysis among older adults at risk of cardiovascular disease: a randomized clinical trial”, PubMed, https://pubmed.ncbi.nlm.nih.gov/17982321/
- “EGb 761 Does Not Affect Blood Coagulation and Bleeding Time in Patients with Probable Alzheimer’s Dementia — Secondary Analysis of a Randomized, Double-Blind Placebo-Controlled Trial”, PMC, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8701823/
- “Impact of Ginkgo biloba drug interactions on bleeding risk and coagulation profiles: A comprehensive analysis”, PLOS One 2025, https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0321804