Herbs & Supplements:
Ginkgo
Ginkgo biloba
Principal Proposed Uses
•
Memory and Mental Function, Alzheimer's Disease, Non-Alzheimer's Dementia, Normal Age-Related Memory Loss, Improving Memory and Mental Function in Younger People
Other Proposed Uses
•
Impaired Circulation in the Legs (Intermittent Claudication), PMS Symptoms, Acute Mountain Sickness, Vertigo, Tinnitus, Sexual Dysfunction in Women Due to Antidepressant Drugs, Macular Degeneration, Assisting Antipsychotic Medications, Depression, Complications of Diabetes, Raynaud's Phenomenon, Assisting Chemotherapy
Traceable back 300 million years, the ginkgo is the oldest surviving species of tree. Although it died out in Europe during the Ice Age, ginkgo survived in China, Japan, and other parts of East Asia. It has been cultivated extensively for both ceremonial and medical purposes, and some particularly revered trees have been lovingly tended for over 1,000 years.
In traditional Chinese herbology, tea made from ginkgo seeds has been used for numerous problems, most particularly asthma and other respiratory illnesses. The leaf was not used. But in the 1950s, German researchers started to investigate the medical possibilities of ginkgo leaf extracts rather than remedies using the seeds. Thus, modern ginkgo preparations are not the same as the traditional Chinese herb, and the comparisons often drawn are incorrect.
What Is Ginkgo Used for Today?
Presently, ginkgo is the most widely prescribed herb in Germany, reaching a total prescription count of over 6 million in 1995.1 German physicians consider it to be as effective as any drug treatment for Alzheimer's disease and other severe forms of memory and mental function decline.2–7 According to some but not all studies, ginkgo may be helpful for seniors with milder forms of memory loss as well.8–14,103 Finally, weak evidence hints that ginkgo (alone or with ginseng) may be helpful for improving memory and mental function in younger people.15–18,90
Germany's Commission E also recommends ginkgo for the treatment of restricted circulation in the legs due to hardening of the arteries known as intermittent claudication.19–22
Chinese research suggests that ginkgo might be able to improve the effectiveness of several medications used for schizophrenia and perhaps reduce their side effects as well.28,93
One study suggests that ginkgo may be helpful in relieving the bloating and fluid retention as well as the emotional disturbance of PMS.29
An intriguing double-blind, placebo-controlled study suggests that ginkgo extracts may be helpful for preventing acute mountain sickness as well as reducing symptoms of cold hands and feet experienced in cold mountain conditions.30,102
Some evidence suggests that ginkgo may be effective for vertigo.31 One study found very weak evidence that it might help sudden hearing loss.32,33 Although study results conflict, on balance the evidence suggests that ginkgo is not helpful for tinnitus (ringing in the ear).34–39,96
Very preliminary evidence suggests that ginkgo extracts might help reverse the impotence or difficulty achieving orgasm caused by certain antidepressant drugs.23–27 One study failed to find benefit, but it appears to have used an inappropriate form of ginkgo.91
Additionally, ginkgo has been proposed as a treatment for macular degeneration, depression, complications of diabetes, and Raynaud's phenomenon, although as yet there is little evidence that it is effective for these purposes. NOTE: There are some concerns regarding ginkgo and diabetes. See Safety Issues for more information.
One study evaluated combination therapy with ginkgo extract and the chemotherapy drug 5FU for the treatment of pancreatic cancer, on the theory that ginkgo might enhance blood flow to the tumor and thereby help 5FU penetrate better.40 The results were promising.
What Is the Scientific Evidence for Ginkgo?
Numerous studies have found that ginkgo extracts can improve circulation.41,42 We don't know exactly how ginkgo does this, but unknown constituents in the herb appear to make the blood more fluid, reduce the tendency toward blood clots, extend the life of a natural blood vessel–relaxing substance, and act as an antioxidant.43,44 However, ginkgo's influence on mental function and other conditions may or may not have anything to do with its effects on circulation.
Impaired Mental Function in the Elderly
In the past, European physicians believed that the cause of mental deterioration with age (senile dementia) was reduced circulation in the brain due to atherosclerosis. Since ginkgo can improve circulation, they assumed that ginkgo was simply getting more blood to brain cells and thereby making them work better.
However, the contemporary understanding of age-related memory loss and mental impairment no longer considers chronically restricted circulation the primary issue. Ginkgo (and other drugs used for dementia) may instead function by directly stimulating nerve-cell activity and protecting nerve cells from further injury,45 although improvement in circulatory capacity may also play a role.
According to a 1992 article published in Lancet, over 40 double-blind, controlled trials had at that time evaluated the benefits of ginkgo in treating various forms of dementia.46 Of these, eight were rated of good quality, involving a total of about 1,000 people and producing positive results in all but one study. The authors of the Lancet article felt that the evidence was strong enough to conclude that ginkgo extract is an effective treatment for this condition.
Most studies reported since 1992 have supported this conclusion, including a large US study published in the Journal of the American Medical Association.47,48,50 The US trial enrolled more than 300 individuals with Alzheimer’s disease or non-Alzheimer’s dementia. Participants were given either 40 mg of ginkgo biloba extract or placebo 3 times daily. The results showed significant (but not dramatic) improvements in the treated group.
One fairly large study of ginkgo extract found no benefit.51 This 24-week, double-blind, placebo-controlled study of 214 individuals with either mild to moderate dementia or ordinary age-associated memory loss found no effect with ginkgo extract at a dose of 240 or 160 mg daily. However, this study has been sharply criticized for a number of serious flaws in its design.94
Ordinary Age-Related Memory Loss
Ginkgo has also been studied for milder forms of memory loss, such as the relatively slight decline in cognitive function that typically accompanies increased age. In six out of eight double-blind studies, use of ginkgo biloba extract significantly improved mental function as compared to placebo.
For example, in a double-blind, placebo-controlled trial, 241 seniors complaining of mildly impaired memory were given either placebo or ginkgo for 24 weeks.52 The results showed that ginkgo produced modest improvements in certain types of memory.
Another double-blind, placebo-controlled trial examined the effects of ginkgo extract in 40 men and women (ages 55 to 86) who did not suffer from any mental impairment.53 Over a 6-week period, the results showed improvements in measurements of mental function.
Benefits were seen in four other trials as well, involving a total of about 135 individuals. 54-57
Set against these positive findings is the 24-week study mentioned above, which found no benefit in ordinary age-related memory loss.58 The reason for this negative outcome may be flaws in this trial’s design.94 However, another study also failed to find any benefit.103 This 6-week trial of 230 healthy individuals over age 60 found that 120 mg of ginkgo biloba extract daily produced no significant improvement in mental function.
Besides these negative trials, there is another weakness in the body of evidence as well. Those studies that did find benefits with ginkgo reported improvements in certain aspects of memory but not in others, and the pattern was not consistent between trials. This tends to decrease the confidence one can place in these outcomes; if ginkgo is really working, its effects on memory should theoretically be reproducible.
Improving Memory and Mental Function in Younger People
Growing (but still highly preliminary) evidence suggests that ginkgo might improve memory and mental function in young people. For example, a 30-day, double-blind, placebo-controlled trial of 50 healthy men and women ranging in age from 18 to 40 years (average 30.4 years) evaluated the effects of 120 mg of gingko extract daily.90 The results showed significant improvements in some measures of memory function. Benefits were also seen in two other small trials. 59,60 However, a double-blind, placebo-controlled trial of 12 women aged 19 to 30 years failed to find any benefit.61
Another study looked at the effects of ginkgo combined with ginseng.62 This 3-month double-blind placebo-controlled trial evaluated various doses of the two herbs combined in 64 individuals complaining of neurasthenia (fatigue and tiredness). The highest dose worked the best. Participants given 200 mg of Panax ginseng and 120 mg of ginkgo daily showed improvements in memory and other aspects of mental function. Strangely, however, this effect appeared to be temporary. Several hours after the dose, memory and mental function actually worsened compared to those given placebo. Researchers speculate that there may be a "payback" for temporarily increased mental function caused by this combination treatment. However, more research is necessary to determine whether this hypothesis has any validity.
Impaired Circulation in the Legs (Intermittent Claudication)
In intermittent claudication, impaired circulation can cause a severe, cramp-like pain in one's legs after walking only a short distance. According to eight double-blind placebo-controlled trials, ginkgo can significantly increase pain-free walking distance.63
One double-blind study enrolled 111 people for 24 weeks.64 Subjects were measured for pain-free walking distance by walking up a 12% slope on a treadmill at 3 kilometers per hour (about 2 miles per hour). At the beginning of treatment, both the placebo and ginkgo (120 mg daily) groups were able to walk about 350 feet without pain. By the end of the trial, both groups had improved (the power of placebo is amazing!), although the ginkgo group improved significantly more: Participants taking ginkgo showed about a 40% increase in pain-free walking distance as compared to only a 20% improvement in the placebo group.
Similar improvements were also seen in a double-blind placebo-controlled trial of 60 individuals who had achieved maximum benefit from physical therapy.65
A 24-week double-blind placebo-controlled study of 74 individuals with intermittent claudication found that ginkgo at a dose of 240 mg per day was more effective than 120 mg per day.66
PMS Symptoms
One double-blind placebo-controlled study evaluated the benefits of Ginkgo biloba extract for women with PMS symptoms.67 This trial enrolled 143 women, 18 to 45 years of age, and followed them for two menstrual cycles. Each woman received either the ginkgo extract (80 mg twice daily) or placebo on day 16 of the first cycle. Treatment was continued until day 5 of the next cycle, and resumed again on day 16 of that cycle.
As compared to placebo, ginkgo significantly relieved major symptoms of PMS, especially breast pain and emotional disturbance.
Macular Degeneration
One preliminary double-blind study suggests that ginkgo may improve macular degeneration.68
Acute Mountain Sickness
Exposure to high altitudes can cause acute mountain sickness. Symptoms include headache, dizziness, shortness of breath, fatigue, and nausea, or, in serious cases, extreme fatigue, impaired motor control, and fluid accumulation in the brain and lungs. In general, the greater the altitude and the more rapid the ascent, the greater the likelihood of severe symptoms.
A placebo-controlled study of 44 mountaineers on a Himalayan expedition found that 160 mg daily of standardized ginkgo extract taken for five days prior to a gradual ascent helped prevent many of these symptoms.74 Unfortunately, the study report does not state whether the trial used a double-blind design.
A double-blind, placebo-controlled trial of 26 individuals tested the effectiveness of ginkgo extract begun one day prior to a rapid ascent, and also found benefit.102
In the first trial, use of ginkgo also appeared to help reduce symptoms of exposure to cold temperatures, such as pain, numbness, and stiffness in the fingers and toes.
Vertigo
A 3-month, double-blind trial of 70 individuals with a variety of vertiginous syndromes found that ginkgo extract given at a dose of 160 mg twice daily produced results superior to placebo.75 By the end of the trial, 47% of the individuals given ginkgo had significantly recovered versus only 18% in the placebo group.
Tinnitus
Studies of Ginkgo biloba extract for treating tinnitus have yielded conflicting results.76–81,96 While some small studies found benefit, the largest and best-designed of these trials failed to find ginkgo effective. In a 12-week, double-blind trial, 1121 individuals with tinnitus
were given either placebo or standardized ginkgo at a dose of 50 mg
3 times daily.82 The results showed no difference between the treated and the placebo groups.
Dosage
The standard dosage of ginkgo is 40 to 80 mg 3 times daily of a 50:1 extract standardized to contain 24% ginkgo-flavone glycosides. Levels of toxic ginkgolic acid and related alkylphenol constituents should be kept under 5 parts per million.
Safety Issues
Ginkgo appears to be relatively safe. Extremely high doses have been given to animals for long periods of time without serious consequences.83 Safety in young children, pregnant or nursing women, or those with severe liver or kidney disease, however, has not been established.
In all the clinical trials of ginkgo up through 1991 combined, involving a total of almost 10,000 participants, the incidence of side effects produced by ginkgo extract was extremely small. There were 21 cases of gastrointestinal discomfort, and even fewer cases of headaches, dizziness, and allergic skin reactions.84
However, ginkgo is a blood thinner, and there have been several case reports of internal bleeding associated with use of ginkgo (spontaneous as well as following surgery).85,86,97-99 For this reason, ginkgo should not be used by those with bleeding disorders such as hemophilia, or by anyone during the periods before or after surgery or labor and delivery.
It seems reasonable to hypothesize that ginkgo might also interact with blood-thinning drugs, amplifying their effects on coagulation. While one study found no interaction between ginkgo and warfarin (Coumadin),100 prudence indicates physician supervision before combining ginkgo with strong blood-thinning drugs such as Coumadin (warfarin), heparin, aspirin, Plavix (clopidogrel), Ticlid (ticlopidine), and Trental (pentoxifylline). (Note: Use of such drugs was prohibited in most of the double-blind trials of ginkgo.) It is also possible that ginkgo could cause bleeding problems if combined with natural blood thinners, such as garlic, policosanol, and high-dose vitamin E.
One study found that when high concentrations of ginkgo were placed in a test tube with hamster sperm and ova, the sperm were less able to penetrate the ova.87 However, since we have no idea whether this much ginkgo can actually come into contact with sperm and ova when they are in the body rather than a test tube, these results may not be meaningful in real life.
The ginkgo extracts approved for use in Germany are processed to remove alkylphenols, including ginkgolic acids, which have been found to be toxic.88 The same ginkgo extracts are available in the United States. However, other ginkgo extracts and whole ginkgo leaf might contain appreciable levels of these dangerous constituents.
Ginkgo seeds contain a toxic substance called 4-methoxypyridoxine (MPN) and may cause seizures.101 Seizures have also been reported with the use of ginkgo extract.89 Two individuals with well-controlled epilepsy experienced recurrent seizures when they took ginkgo extract. One possible explanation is contamination of ginkgo leaf products with ginkgo seeds. Another possibility has been proposed as well: The drug tacrine (also used to improve memory) has been associated with seizures, and ginkgo may affect the brain in ways similar to tacrine.92
There are some indications that ginkgo might alter insulin release in individuals with diabetes.95 The effect appears to be rather complex; the herb may cause some increase in insulin output, and yet might actually lower insulin levels overall through its effects on the liver and perhaps on oral medications used for diabetes. Until this situation is clarified, individuals with diabetes should use ginkgo only under physician supervision.
Interactions You Should Know About
If you are taking
- Blood-thinning drugs such as Coumadin (warfarin), heparin, aspirin, Plavix (clopidogrel), Ticlid (ticlopidine), or Trental (pentoxifylline): Simultaneous use of ginkgo might cause bleeding problems.
- Natural substances with blood-thinning properties, such as garlic, phosphatidylserine, orhigh-dose vitamin E: It is possible that, again, simultaneous use of ginkgo might cause bleeding problems.
- Antidepressant drugs, especially in the SSRI family: Ginkgo might remedy sexual side effects such as impotence or inability to achieve orgasm.
- Antipsychotic medications in the phenothiazine family as well as atypical antipsychotic drugs (such as clozapine and olanzapene): Ginkgo might help them work better with fewer side effects.
View References
Last reviewed September 2002 by Medical Review Board
Back to Top
