Ginkgo biloba is generally safe and well-tolerated when taken as a standardized leaf extract at doses up to 240 mg per day. Most people experience no side effects, and clinical trials consistently show a mild adverse event profile. That said, ginkgo does carry real risks for certain groups, particularly people on blood thinners, those with seizure disorders, and anyone approaching surgery.
Common Side Effects
The side effects reported in clinical trials are mild and relatively infrequent. They include headache, heart palpitations, digestive upset, constipation, and allergic skin reactions. These tend to resolve on their own and rarely cause people to stop taking the supplement. In studies testing both 120 mg and 240 mg daily doses over 24 weeks, both were described as safe and well tolerated.
Bleeding Risk and Blood Thinners
This is the most important safety concern with ginkgo. The supplement can reduce the ability of blood platelets to clump together, which is one of the early steps in forming a clot. On its own, this effect appears modest. A systematic review found no significant changes in standard clotting measures. But when ginkgo is combined with blood-thinning medications, the picture changes considerably.
A large study of veterans taking warfarin found that adding ginkgo increased the risk of a bleeding event by 38%. Several case reports have also linked ginkgo use to serious bleeding episodes, including bleeding inside the skull. If you take warfarin, aspirin, or any other anticoagulant or antiplatelet drug, ginkgo is not a casual addition to your routine.
Ginkgo and Seizure Medications
People taking anti-seizure medications should be especially cautious. Ginkgo can speed up the activity of certain liver enzymes (specifically CYP2C19) that break down common seizure drugs. This means the medications get cleared from your body faster, potentially dropping to levels too low to prevent seizures. In one fatal case, a person taking two standard anti-seizure medications was found at autopsy to have dangerously low blood levels of both drugs while also taking ginkgo and other supplements.
There’s a second layer of risk here: ginkgo nuts (the seeds, not the leaf extract) contain a neurotoxin called ginkgotoxin that can directly trigger seizures by interfering with vitamin B6 activity in the brain. Standardized leaf extracts contain far less of this compound than raw seeds, but the combination of enzyme effects and even trace amounts of the toxin makes ginkgo a poor match for anyone with epilepsy or a seizure history.
How Ginkgo Affects Other Medications
Beyond blood thinners and seizure drugs, the question of whether ginkgo broadly interferes with medication metabolism has gotten mixed answers over the years. Early lab studies using animal tissue and human cells in test tubes suggested ginkgo could inhibit or rev up several of the major liver enzymes responsible for processing drugs. This raised concerns about interactions with a wide range of medications.
However, a controlled study in healthy volunteers tested the standardized extract EGb 761 against five major drug-processing enzymes and found no meaningful inhibition or induction of any of them at either 120 mg or 240 mg daily doses. The results suggest that for most people taking most medications, ginkgo is unlikely to cause the kind of broad metabolic interference that, say, grapefruit juice is known for. Still, the specific interactions with blood thinners and seizure drugs are well enough documented to take seriously, even if the general enzyme picture looks reassuring.
Surgery and Ginkgo
Because of its effects on platelet function, ginkgo can increase bleeding during and after surgical procedures. Both the American Society of Anesthesiologists and the American Association of Nurse Anesthetists recommend stopping herbal medications, ginkgo included, one to two weeks before any elective surgery. If you have a procedure scheduled, mention ginkgo use to your surgical team even if they don’t specifically ask about supplements.
Pregnancy, Breastfeeding, and Children
There is essentially no safety data on ginkgo use during breastfeeding. The National Institutes of Health’s lactation database notes that no published studies exist on how ginkgo affects nursing mothers, breast milk composition, or breastfed infants. The same data gap applies to pregnancy. Without evidence to confirm safety, ginkgo is not recommended for pregnant or breastfeeding women.
Ginkgo Seeds vs. Leaf Extract
An important distinction most people miss: the standardized leaf extract sold as a supplement is very different from raw ginkgo seeds (sometimes called ginkgo nuts), which are eaten in some East Asian cuisines. The seeds contain ginkgotoxin, a compound that works against vitamin B6 in the brain. Eating too many can cause vomiting, seizures, and loss of consciousness. Reported cases describe generalized convulsions followed by confusion, along with dizziness and severe weakness. Roasting reduces but does not eliminate the toxin. The leaf extract used in capsules and tablets contains only trace levels of ginkgotoxin and is not associated with these poisoning events at normal doses.
What “Standardized Extract” Means
Most clinical research on ginkgo uses a specific formulation called EGb 761, standardized to contain set percentages of its active compounds. The typical dose range in studies is 120 to 240 mg per day, with 240 mg being the upper recommended limit. If you’re choosing a supplement, look for products that specify standardized extract percentages on the label rather than just listing raw ginkgo leaf powder, which can vary widely in potency and composition.
In the United States, ginkgo is sold as a dietary supplement, not a drug. The FDA does not evaluate supplements for safety or effectiveness before they reach store shelves. This means quality control depends entirely on the manufacturer, and products can vary significantly. Third-party testing seals from organizations like USP, NSF, or ConsumerLab offer some reassurance that what’s on the label matches what’s in the bottle.
Who Should Avoid Ginkgo
- People on blood thinners (warfarin, aspirin, or similar drugs), due to a meaningful increase in bleeding risk
- People with seizure disorders, especially those on anti-seizure medications whose blood levels could drop
- Anyone within two weeks of surgery, to reduce the chance of excess bleeding
- Pregnant or breastfeeding women, due to a complete lack of safety data
For most healthy adults not in these groups, ginkgo leaf extract at standard doses has a well-established safety record across decades of clinical use. The side effects are mild and uncommon, and the major risks are specific and avoidable if you know about them beforehand.