Ginkgo (Ginkgo biloba) is one of the oldest living tree species. It is also tops in scientific studies and in purchases. In Europe and the United States, ginkgo supplements are among the best-selling herbal medications.

Ginkgo has a long history of being used in traditional medicine to treat blood disorders and improve memory, and it's best known today as way to potentially keep your memory sharp. There is some scientific evidence to back that up. Laboratory studies have shown that ginkgo improves blood circulation by opening up blood vessels and making blood less sticky. It's also an antioxidant. 

For those reasons, ginkgo may improve vein and eye health. Although not all studies agree, ginkgo may help treat dementia (including Alzheimer's disease) and intermittent claudication, or poor circulation in the legs. It may also protect memory in older adults.

Ginkgo leaves have two types of chemicals (flavonoids and terpenoids) that are antioxidants. In your body, harmful particles called free radicals build up as you age, and may contribute to heart disease, cancer, and Alzheimer's disease. Antioxidants like those found in ginkgo fight off free radicals, and stop them from damaging DNA and other cells.

Ginkgo biloba is the oldest living tree species. A single tree can live as long as 1,000 years and grow to a height of 120 feet. It has short branches with fan-shaped leaves and inedible fruits that smell bad. The fruit has an inner seed, which may be poisonous. Ginkgos are tough, hardy trees and are sometimes planted along urban streets in the United States. The leaves turn brilliant colors in the fall.

Although Chinese herbal medicine has used both the ginkgo leaf and seed for thousands of years, modern research has focused on the standardized Ginkgo biloba extract (GBE) made from the dried green leaves. This standardized extract is highly concentrated and seems to treat health problems (particularly circulatory problems) better than the non-standardized leaf alone.

Scientists have found more than 40 components in ginkgo. But only two are believed to act as medicine: flavonoids and terpenoids. Flavonoids are plant-based antioxidants. Laboratory and animal studies show that flavonoids protect the nerves, heart muscle, blood vessels, and retina from damage. Terpenoids (such as ginkgolides) improve blood flow by dilating blood vessels and reducing the stickiness of platelets.

Based on studies conducted in laboratories, animals, and people, ginkgo is used for the following:

Dementia and Alzheimer's disease

Ginkgo is widely used in Europe for treating dementia. At first, doctors thought it helped because it improves blood flow to the brain. Now more study suggests it may protect nerve cells that are damaged in Alzheimer's disease. A number of studies have found that ginkgo has a positive effect on memory and thinking in people with Alzheimer's or vascular dementia.

Studies suggest that ginkgo may help people with Alzheimer's disease:

• Improve thinking, learning, and memory (cognitive function)
• Have an easier time doing day to day activities
• Improve social behavior
• Have fewer feelings of depression

Several studies have found that ginkgo may work as well as some prescription Alzheimer's medications to delay the symptoms of dementia. It has not been tested against all of the drugs prescribed to treat Alzheimer's.

However, one of the longest and best-designed studies found ginkgo was no better than placebo in reducing Alzheimer's symptoms. In a 2008 study, 176 people in the United Kingdom with Alzheimer's took either ginkgo or placebo for 6 months. At the end of the study there was no difference in mental function or quality of life between the groups.

Ginkgo is sometimes suggested to prevent Alzheimer's and dementia, as well, and some studies have suggested it might help. But in 2008, a well-designed study (the GEM study) with more than 3,000 elderly people found that ginkgo was no better than placebo in preventing dementia or Alzheimer's.

Intermittent Claudication

Because ginkgo improves blood flow, it has been studied in people with intermittent claudication, or pain caused by reduced blood flow to the legs. People with intermittent claudication have a hard time walking without feeling extreme pain. An analysis of eight studies showed that people taking ginkgo tended to walk about 34 meters farther than those taking placebo. In fact, ginkgo has been shown to work as well as a prescription medication in improving pain-free walking distance. However, regular walking exercises work better than ginkgo in improving walking distance.

Anxiety

One preliminary study found that ginkgo might help relieve anxiety. People with generalized anxiety disorder and adjustment disorder who took a specific extract of ginkgo had fewer anxiety symptoms than those who took placebo.

Glaucoma

One small study found that people with glaucoma who took 120 mg of ginkgo daily for 8 weeks had improvements in their vision.

Memory and Thinking

Ginkgo is widely touted as a "brain herb." Some studies show that it does help improve memory in people with dementia. It's not as clear whether ginkgo helps memory in healthy people who have normal, age-related memory loss. Some studies have found slight benefits, while other studies have found it didn't help at all. Some studies have found that ginkgo helps improve memory and thinking in young and middle-aged people who are healthy. The dose that works best seems to be 240 mg per day. There's no proof that taking ginkgo will help protect against dementia. Ginkgo is often added to nutrition bars, soft drinks, and fruit smoothies to boost memory and enhance mental performance, although such small amounts probably don't help.

Macular Degeneration

The flavonoids found in ginkgo may help stop or reduce some problems with the retina, the back part of the eye. Macular degeneration, often called age-related macular degeneration or AMD, is an eye disease that affects the retina. The number one cause of blindness in the Unites States, AMD is a degenerative eye disease that gets worse as time goes on. Some studies suggest that ginkgo may help preserve vision in those with AMD.

Premenstrual Syndrome (PMS)

Two studies with a somewhat complicated dosing schedule found that ginkgo helped reduced PMS symptoms. Women in the studies took ginkgo beginning on day 16 of their menstrual cycle and stopped taking it after day 5 of their next cycle, then took it again on day 16.

Raynaud's Phenomenon

One well-designed study found that people with Raynaud's phenomenon who took ginkgo over a 10-week period had fewer symptoms than those who took placebo. More studies are needed.

• Standardized extracts containing 24 - 32% flavonoids (also known as flavone glycosides or heterosides) and 6 - 12% terpenoids (triterpene lactones)
• Capsules
• Tablets
• Liquid extracts (tinctures, fluid extracts, glycerites)
• Dried leaf for teas

Pediatric

Ginkgo should not be given to children.

Adult

It can take 4 - 6 weeks to see any effects from ginkgo. Ask your doctor to help you find the right dose.

Memory problems and Alzheimer's disease: Many studies have used 120 - 240 mg daily in divided doses, standardized to contain 24 - 32% flavone glycosides (flavonoids or heterosides) and 6 - 12% triterpene lactones (terpenoids).

Intermittent claudication: Studies have used 120 - 240 mg per day.

The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, can trigger side effects and interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care, under the supervision of a health care provider qualified in the field of botanical medicine.

Ginkgo usually has few side effects. In a few cases, stomach upset, headaches, skin reactions, and dizziness were reported.

There have been reports of internal bleeding in people who take ginkgo. It's not clear whether the bleeding was due to ginkgo or some other reasons, such as a combination of ginkgo and blood-thinning drugs. Researchers aren’t sure, because different studies have found different results. You should ask your doctor before taking ginkgo if you also take blood-thinning drugs.

Stop taking ginkgo at least 36 hours before surgery or dental procedures due to the risk of bleeding. Tell your doctor or dentist that you take ginkgo.

People who have epilepsy should not take ginkgo, because it might cause seizures.

Pregnant and breastfeeding women should not take ginkgo.

People who have diabetes should ask their doctor before taking ginkgo.

Do not eat Ginkgo biloba fruit or seed.

Ginkgo may interact with some prescription and non-prescription medications. If you are taking any of the following medications, you should not use ginkgo without first talking to your health care provider:

Medications broken down by the liver -- Ginkgo can interact with some medications that are processed through the liver. If you take any prescription medications, ask your doctor before taking ginkgo.

Seizure medications (anticonvulsants) -- High doses of ginkgo could make anti-seizure drugs not work as well. These drgs include carbamazepine (Tegretol) and valproic acid (Depakote).

Antidepressants -- Taking ginkgo along with a kind of antidepressant called selective serotonin reuptake inhibitors (SSRIs) may increase the risk of serotonin syndrome, a life-threatening condition. Also, ginkgo may strengthen both the good and bad effects of antidepressants known as MAOIs, such as phenelzine (Nardil). SSRIs include:

• Citalopram (Celexa)
• Escitalopram (Lexapro)
• Fluoxetine (Prozac)
• Fluvoxamine (Luvox)
• Paroxetine (Paxil)
• Sertraline (Zoloft)

Medications for high blood pressure -- Ginkgo may lower blood pressure, so taking it with blood pressure medications may cause blood pressure to drop too low. There has been a report of an interaction between ginkgo and nifedipine (Procardia), a calcium channel blocker used for blood pressure and heart rhythm problems.

Blood-thinning medications -- Ginkgo may raise the risk of bleeding, especially if you take blood-thinners such as warfarin (Coumadin), clopidogrel (Plavix), and aspirin.

Alprazolam (Xanax) -- Ginkgo may make Xanax, and drug taken to treat anxiety, not work as well.

Ibuprofen (Advil, Motrin) -- Like ginkgo, the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen also raises the risk of bleeding. There has been bleeding in the brain reported when using a ginkgo product and ibuprofen.

Medications to lower blood sugar -- Ginkgo may raise or lower insulin levels and blood sugar levels. If you have diabetes, you should not use ginkgo without first talking to your doctor.

Cylosporine -- Ginkgo biloba may help protect the cells of the body during treatment with the drug cyclosporine, which suppresses the immune system.

Thiazide diuretics (water pills) -- There is one report of a person who took a thiazide diuretic and ginkgo developing high blood pressure. If you take thiazide diuretics, ask your doctor before taking ginkgo.

Trazodone -- There is one report of an elderly Alzheimer's patient going into a coma after taking ginkgo and trazodone (Desyrel), an antidepressant medication.

Amieva H, Meillon C, Helmer C, Barberger-Gateau P, Dartigues JF. Ginkgo biloba extract and long-term cognitive decline: a 20-year follow-up population-based study. PLoS One. 2013;8(1):e52755. doi: 10.1371/journal.pone.0052755. Epub 2013 Jan 11.

Aruna D, Naidu MU.Pharmacodynamic interaction studies of Ginkgo biloba with cilostazol and clopidogrel in healthy human subjects. Br J Clin Pharmacol. 2006 Sep 29; [Epub ahead of print].

Ashton, A. K., Ahrens, K., Gupta, S., and Masand, P. S. Antidepressant-induced sexual dysfunction and Ginkgo Biloba. Am J Psychiatry. 2000;157(5):836-837.

Birks J, Grimley Evans J. Ginkgo biloba for cognitive impairment and dementia. Cochrane Database Syst Rev. 2009 Jan 21;(1):CD003120. Review.

Cheuvront, S. N. and Carter, R., III. Ginkgo and memory. JAMA. 2-5-2003;289(5):547-548.

Christen Y. Oxidative stress and Alzheimer's disease. Am J Clin Nutr. 2000;71(suppl):621S-629S.

Choi WS, Choi CJ, Kim KS, Lee JH, Song CH, Chung JH, et al. To compare the efficacy and safety of nifedipine sustained release with Ginkgo biloba extract to treat patients with primary Raynaud's phenomenon in South Korea; Korean Raynaud study (KOARA study). Clin Rheumatol. 2009 Jan 22. [Epub ahead of print]

Cieza, A., Maier, P., and Poppel, E. Effects of Ginkgo biloba on mental functioning in healthy volunteers. Arch Med Res. 2003;34(5):373-381.

Davydov L and Stirling AL. Stevens-Johnson syndrome with Ginkgo biloba. J Herbal Pharmacother. 2001;1(3):65-69.

DeKosky ST, Williamson JD, Fitzpatrick AL, Kronmal RA, Ives DG, Saxton JA, et al; Ginkgo Evaluation of Memory (GEM) Study Investigators. Ginkgo biloba for prevention of dementia: a randomized controlled trial. JAMA. 2008 Nov 19;300(19):2253-62. Erratum in: JAMA. 2008 Dec 17;300(23):2730.

Diamond BJ, Shiflett SC, Feiwel N, et al. Ginkgo biloba extract: mechanisms and clinical indications. Arch Phys Med Rehabil. 2000;81:669-678.

Drew S, Davies E. Effectiveness of Ginkgo biloba in treating tinnitus: double blind, placebo controlled trial. BMJ. 2001;322(7278):73.

Engelsen, J., Nielsen, J. D., and Hansen, K. F. [Effect of Coenzyme Q10 and Ginkgo biloba on warfarin dosage in patients on long-term warfarin treatment. A randomized, double-blind, placebo-controlled cross-over trial]. Ugeskr.Laeger. 4-28-2003;165(18):1868-1871.

Evans JR. Ginkgo biloba extract for age-related macular degeneration. Cochrane Database Syst Rev. 2013 Jan 31;1:CD001775. doi: 10.1002/14651858.CD001775.pub2. Review.

Hartley, D. E., Elsabagh, S., and File, S. E. Gincosan (a combination of Ginkgo biloba and Panax ginseng): the effects on mood and cognition of 6 and 12 weeks' treatment in post-menopausal women. Nutr Neurosci. 2004;7(5-6):325-333.

Hilton, M. and Stuart, E. Ginkgo biloba for tinnitus. Cochrane Database Syst Rev. 2004;(2):CD003852.

Horsch, S. and Walther, C. Ginkgo biloba special extract EGb 761 in the treatment of peripheral arterial occlusive disease (PAOD)--a review based on randomized, controlled studies. Int.J Clin Pharmacol Ther. 2004;42(2):63-72.

Huang, S. Y., Jeng, C., Kao, S. C., Yu, J. J., and Liu, D. Z. Improved haemorrheological properties by Ginkgo biloba extract (Egb 761) in type 2 diabetes mellitus complicated with retinopathy. Clin.Nutr. 2004;23(4):615-621.

Johnson SK, Diamond BJ, Rausch S, Kaufman M, Shiflett SC, Graves L. The effect of Ginkgo biloba on functional measures in multiple sclerosis: a pilot randomized controlled trial. Explore (NY). 2006;2(1):19-24.

Kenney C, Norman M, Jacobson M, and et al. A double-blind, placebo-controlled, modified crossover pilot study of the effects of Ginkgo biloba on cognitive and functional abilities in multiple sclerosis. American Academy of Neurology 54th Annual Meeting. April 13-20 2002;P06.081.

Kohler, S., Funk, P., and Kieser, M. Influence of a 7-day treatment with Ginkgo biloba special extract EGb 761 on bleeding time and coagulation: a randomized, placebo-controlled, double-blind study in healthy volunteers. Blood Coagul.Fibrinolysis. 2004;15(4):303-309.

Le Bars PL, Kieser M, Itil KZ. A 26-week analysis of a double-blind, placebo-controlled trial of the Ginkgo biloba extract EGb761 in dementia. Dement Geriatr Cogn Disord. 2000;11:230-237.

Mantle D, Pickering AT, Perry AK. Medicinal plant extracts for the treatment of dementia: a review of their pharmacology, efficacy and tolerability. CNS Drugs. 2000;13:201-213.

Mauro, V. F., Mauro, L. S., Kleshinski, J. F., Khuder, S. A., Wang, Y., and Erhardt, P. W. Impact of ginkgo biloba on the pharmacokinetics of digoxin. Am.J Ther 2003;10(4):247-251.

May BH, Lit M, Xue CC, Yang AW, Zhang AL, Owens MD, et al. Herbal medicine for dementia: a systematic review. Phytother Res. 2008 Dec 11;23(4):447-459.

May BH, Yang AW, Zhang AL, Owens MD, Bennett L, Head R, et al. Chinese herbal medicine for Mild Cognitive Impairment and Age Associated Memory Impairment: a review of randomised controlled trials. Biogerontology. 2009 Apr;10(2):109-23. Epub 2008 Aug 21.

Mazza M, Capuano A, Bria P, Mazza S. Ginkgo biloba and donepezil: a comparison in the treatment of Alzheimer's dementia in a randomized placebo-controlled double-blind study. Eur J Neurol. 2006;13(9):981-5.

McCarney R, Fisher P, Iliffe S, van Haselen R, Griffin M, van der Meulen J, Warner J. Ginkgo biloba for mild to moderate dementia in a community setting: a pragmatic, randomised, parallel-group, double-blind, placebo-controlled trial. Int J Geriatr Psychiatry. 2008 Dec;23(12):1222-30.

Moher D, Pham B, Ausejo M, Saenz A, Hood S, Barber GG. Pharmacological management of intermittent claudication: a meta-analysis of randomised trials. Drugs. 2000;59(5):1057-1070.

Nathan, P. J., Harrison, B. J., and Bartholomeusz, C. Ginkgo and memory. JAMA. 2-5-2003;289(5):546-548.

Oh SM, Chung KH. Antiestrogenic activities of Ginkgo biloba extracts. J Steroid Biochem Mol Biol. 2006;100(4-5):167-76.

Persson, J., Bringlov, E., Nilsson, L. G., and Nyberg, L. The memory-enhancing effects of Ginseng and Ginkgo biloba in healthy volunteers. Psychopharmacology (Berl) 2004;172(4):430-434.

Pittler MH, Ernst E. Ginkgo biloba extract for the treatment of intermittent claudication: a meta-analysis of randomized trials. Am J Med. 2000;108(4):276-281.

Schneider LS, DeKosky ST, Farlow MR, Tariot PN, Hoerr R, Kieser M. A randomized, double-blind, placebo-controlled trial of two doses of Ginkgo biloba extract in dementia of the Alzheimer's type. Curr Alzheimer Res. 2005;2(5):541-51.

Snitz BE, et al; Ginkgo Evaluation of Memory (GEM) Study Investigators. Ginkgo biloba for preventing cognitive decline in older adults: a randomized trial. JAMA. 2009 Dec 23;302(24):2663-70.

Trick, L., Boyle, J., and Hindmarch, I. The effects of Ginkgo biloba extract (LI 1370) supplementation and discontinuation on activities of daily living and mood in free living older volunteers. Phytother Res. 2004;18(7):531-537.

Van Dongen, M., van Rossum, E., Kessels, A., Sielhorst, H., and Knipschild, P. Ginkgo for elderly people with dementia and age-associated memory impairment: a randomized clinical trial. J Clin Epidemiol. 2003;56(4):367-376.

Vellas, B., and Grandjean, H. Association of Alzheimer's disease onset with ginkgo biloba and other symptomatic cognitive treatments in a population of women aged 75 years and older from the EPIDOS study. J Gerontol A Biol.Sci.Med Sci. 2003;58(4):372-377.

Vellas B, Coley N, Ousset PJ, et al.; GuidAge Study Group. Long-term use of standardised Ginkgo biloba extract for the prevention of Alzheimer's disease (GuidAge): a randomised placebo-controlled trial. Lancet Neurol. 2012 Oct;11(10):851-9. doi: 10.1016/S1474-4422(12)70206-5. Review.

Wang BS, Wang H, Song YY, Qi H, Rong ZX, Wang BS, Zhang L, Chen HZ. Effectiveness of standardized ginkgo biloba extract on cognitive symptoms of dementia with a six-month treatment: a bivariate random effect meta-analysis. Pharmacopsychiatry. 2010 May;43(3):86-91.

Zhang L, Mao W, Guo X, Wu Y, Li C, Lu Z, Su G, Li X, Liu Z, Guo R, Jie X, Wen Z, Liu X. Ginkgo biloba Extract for Patients with Early Diabetic Nephropathy: A Systematic Review. Evid Based Complement Alternat Med. 2013;2013:689142. doi: 10.1155/2013/689142. Epub 2013 Feb 24.