Ginkgo

Is ginkgo safe?

For most adults, ginkgo leaf extract is one of the better-studied herbs, and it is not very toxic. NCCIH notes that leaf extracts have been used safely in studies lasting up to six years, including the US Ginkgo Evaluation of Memory study of more than 3,000 people aged 75 and older. Headache is the most common side effect, followed by dizziness and stomach upset.

What lowers its score is not the herb itself. It affects blood clotting, so it matters for anyone on a blood thinner or facing surgery. It has a short list of real drug interactions. And much of what is sold as ginkgo in supplement shops is not what the label says.

Bleeding and blood thinners

Ginkgo can reduce the ability of platelets to clump together. The European Medicines Agency's herbal monograph lists reports of bleeding in the eye, nose, brain and gut, with unknown frequency. It is cautious rather than alarmed: studies with warfarin have not shown a clear interaction, but the EMA still advises monitoring when you start, stop, change the dose or switch brand.

The same applies to antiplatelet drugs such as clopidogrel and aspirin, and to NSAIDs such as ibuprofen. People with a bleeding disorder should not take ginkgo without a doctor's agreement, and everyone should stop it 3 to 4 days before surgery. Stacking ginkgo with other supplements that affect clotting, such as high-dose fish oil or turmeric, adds up.

Other drug interactions

Drug	Effect in the EMA monograph
Efavirenz (HIV)	Lower efavirenz levels; combination not recommended
Nifedipine (blood pressure)	Peak level up to 100% higher in some people, with dizziness and flushing
Dabigatran (blood thinner)	Possible higher exposure via gut P-glycoprotein
Anticoagulants and antiplatelets	Effect may be changed

People with epilepsy are a separate case. The monograph says further seizures caused by ginkgo "cannot be excluded". If you take any regular medicine, ask your doctor or pharmacist before adding ginkgo.

The cancer finding in mice

The US National Toxicology Program gave a ginkgo leaf extract to rats and mice for two years and found clear evidence of liver cancer in mice; a rat study found thyroid tumours. The International Agency for Research on Cancer later classified ginkgo extract as possibly carcinogenic to humans (group 2B).

The EMA's view is that these tumours come from very high doses of a substance that switches on liver enzymes, a mechanism specific to rodents, and are not relevant to people at normal doses. There is no human evidence of cancer from ginkgo. We score it as a real but limited concern rather than a reason to avoid the herb.

Most ginkgo supplements are adulterated

This is ginkgo's weakest point. Genuine extract is expensive to make: the licensed European standard uses about 35 to 67 kg of leaves for each kilogram of extract. Cheaper products are often topped up with rutin or quercetin, flavonoids from buckwheat or the sophora tree, to pass simple tests for total flavonoids.

Two independent studies show how common this is. In 2016, UK researchers found that 33 of 35 ginkgo products had raised rutin or quercetin or too little of ginkgo's own compounds. In 2019, a fingerprinting study found adulterants in 48 of 59 ginkgo dietary supplements. The added flavonoids are not dangerous in themselves, but you are not getting the product that was tested in trials.

How to choose and use it

• Pick a product that states a standardised dry extract, ideally a licensed herbal medicine in the EU or UK (a THR or marketing authorisation number on the pack) or one with USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary status in the US.
• The licensed dose is 240 mg a day, split into one or two doses, for at least 8 weeks. If there is no benefit after three months, there is little reason to continue.
• Do not eat raw ginkgo seeds, and keep them away from children.
• Avoid it in pregnancy and while breastfeeding.
• Stop 3 to 4 days before surgery or dental work involving bleeding.

How we scored it

Dose safety (80) and regulatory actions (78) are strong: mild side effects, years of trial data and no bans. Product quality (42) is the weakest factor because adulteration is widespread outside licensed medicines, and interactions (58) reflect blood thinners and a few specific drugs. Ginkgo sits close to turmeric, another popular herb with patchy product quality, and well above St John's wort on interactions.