What is ginkgo biloba? A plain-English guide

Ginkgo biloba, often just called ginkgo, is a tree that drops its leaves every year [1].

Its seeds and leaves have been used in traditional herbal practice for thousands of years [6]. A 2017 review describes its extract as one of the most widely sold herbal supplements in the world [6].

The leaf, usually as an extract (a concentrate made from the leaves), is the most common form used [1]. Health Canada's guide for licensed products calls for standardized extracts, with set levels of two groups of plant chemicals [4].

Ginkgo has been promoted with claims that it can improve thinking in healthy people [1]. Researchers have tested it for memory, attention and other thinking skills in healthy adults [2], and for thinking over time in older adults [3].

NCCIH, part of the US National Institutes of Health, says it is uncertain whether ginkgo affects thinking in healthy people [1].

Does ginkgo help memory in healthy people?

Evidence grade for memory: N, no benefit shown. Why this grade

A 2012 meta-analysis (a study that pools the results of many trials) looked at memory in 13 randomized controlled trials [2]. In this kind of trial, people are put into groups by chance, so the groups can be fairly compared. Together the trials included 1,132 healthy people, and the effect on memory was close to zero [2]. It did not change with the dose, the length of the trial or the age of the people taking part [2].

In one 6-week trial, 230 healthy adults over 60 got ginkgo or a matching placebo by chance [8]. Neither they nor the researchers knew who got which [8]. The trial found no clear differences between the groups on any measure, including memory tests [8].

Does ginkgo help attention?

Evidence grade for attention: N, no benefit shown. Why this grade

In the 2012 meta-analysis, 8 trials with 910 healthy people measured attention, and the effect was close to zero [2].

In one small study, 20 healthy young volunteers took single doses of Pharmaton's standardized extract and a placebo, each in turn [9]. After 240 mg or 360 mg, a "speed of attention" score improved compared with placebo [9]. The same trial found other changes too, some better and some worse [9].

A 2007 review of 15 trials in healthy people under 60 found that single-dose results like these were either not repeated or were contradicted [7]. It found no convincing evidence of a clear benefit for any thinking skill, after one dose or longer use [7].

Does ginkgo affect thinking in older adults?

Evidence grade for global cognition: N, no benefit shown. Why this grade

The GEM trial followed 3,069 adults aged 72 to 96 at 6 US medical centers [3]. They were put into groups by chance, and neither they nor the researchers knew who got ginkgo [3]. Some already had mild thinking problems at the start [3]. They took 120 mg of ginkgo extract twice a day, or a placebo that looked the same [3]. The median time in the trial (the middle value) was 6.1 years [3].

The yearly change in thinking test scores did not differ between the two groups in any area, including memory [3]. Results did not differ by age, sex, education, or whether people had mild thinking problems at the start [3].

The trial was funded by grants from two US National Institutes of Health centers [3]. Schwabe Pharmaceuticals gave the tablets and placebos [3]. The company had no role in the design, analysis or approval of the paper [3]. It was given the paper to check facts about the product [3].

To see what each grade means, read how we grade evidence.

Table: Doses used in studies (not a recommendation)

These are amounts used in research, not advice. Talk to a clinician before trying ginkgo.

NCCIH says ginkgo leaf extract is likely safe for most adults in moderate amounts [1]. It has been used safely in studies lasting up to 6 years [1]. NCCIH lists dizziness, stomach and gut symptoms, and headache as the most common side effects [1]. EMA, the European medicines regulator, reports headache as the most common side effect in people using ginkgo medicines for mild dementia [5].

Regulators name bleeding and blood thinners as the main cautions [4][5]. EMA reports that bleeding in the eye, nose, brain or gut has been reported [5]. NCCIH says ginkgo may raise the risk of bleeding in people taking blood thinners, such as warfarin [1].

A 2011 meta-analysis of 18 trials looked at blood clotting tests in 1,985 adults, most of them patients [10]. These lab tests did not point to a higher bleeding risk with standardized extracts [10]. These are lab measures, not bleeding events. Health Canada and EMA still list the cautions below [4][5].

Fresh ginkgo seeds are toxic when eaten, and serious side effects have also occurred after eating roasted seeds or the crude plant [1]. This is a separate risk from the leaf extract [1][6].

In 2-year studies by the US National Toxicology Program, one ginkgo leaf extract led to more liver tumors in mice [6]. These are animal results [6]. The International Agency for Research on Cancer lists ginkgo leaf extract as a possible cause of cancer in humans [6]. The review reporting both was funded by the US FDA [6].

Talk to a clinician or pharmacist before trying ginkgo.

• People taking blood thinners. Health Canada says not to use ginkgo products with blood thinners or other products that affect clotting [4]. EMA advises talking to a doctor first [5].
• People having surgery. Health Canada says not to use ginkgo products when having surgery [4].
• People who are pregnant or breastfeeding. Health Canada asks them to check with a health professional first [4]. NCCIH says ginkgo may be unsafe in pregnancy [1].
• Children. EMA says ginkgo leaf medicines should only be used in adults [5].
• People taking medicines for diabetes, high blood pressure or seizures. Health Canada asks them to check with a health professional first [4].

If you take any of these medicines, talk to your doctor or pharmacist before combining them with ginkgo.