Ginkgo (Ginkgo biloba) is one of the oldest living tree species. Most ginkgo products are made with extract prepared from its fan-shaped leaves.

The most helpful components of ginkgo are believed to be flavonoids, which have powerful antioxidant qualities, and terpenoids, which help improve circulation by dilating blood vessels and reducing the "stickiness" of platelets.

Ginkgo is commonly available as an oral tablet, extract, capsule or tea. Don't eat raw or roasted ginkgo seeds, which can be poisonous.

Most research on ginkgo focuses on its effect on dementia, memory and pain caused by too little blood flow (claudication).

Research on ginkgo use for specific conditions shows:

• Dementia. There isn't enough evidence to support the use of ginkgo to prevent dementia or treat people with mild cognitive impairment.
• Claudication. A review of the research suggests that taking ginkgo has no significant benefits for people with this condition.

Ginkgo's effect on memory enhancement has had conflicting results. While some evidence suggests that ginkgo extract might modestly improve memory in healthy adults, most studies indicate that ginkgo doesn't improve memory, attention or brain function.

When used orally in moderate amounts, ginkgo appears to be safe for most healthy adults.

Ginkgo can cause:

• Headache
• Dizziness
• Heart palpitations
• Upset stomach
• Constipation
• Allergic skin reactions

Don't eat raw or roasted ginkgo seeds, which can be poisonous.

If you are epileptic or prone to seizures, avoid ginkgo. Large amounts of ginkgotoxin can cause seizures. Ginkgotoxin is found in ginkgo seeds and, to a lesser extent, ginkgo leaves.

If you are older, have a bleeding disorder or are pregnant, don't take ginkgo. The supplement might increase your risk of bleeding. If you're planning to have surgery, stop taking ginkgo two weeks beforehand.

Ginkgo might interfere with the management of diabetes. If you take ginkgo and have diabetes, closely monitor your blood sugar levels.

Some research has shown that rodents given ginkgo had an increased risk of developing liver and thyroid cancers.

Possible interactions include:

• Alprazolam (Xanax). Taking ginkgo with this drug used to relieve symptoms of anxiety might reduce the drug's effectiveness.
• Anticoagulants and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Taking ginkgo with them might increase your risk of bleeding.
• Anticonvulsants and seizure threshold lowering drugs, herbs and supplements. Large amounts of ginkgotoxin can cause seizures. Ginkgotoxin is found in ginkgo seeds and, to a lesser extent, ginkgo leaves. It's possible that taking ginkgo could reduce the effectiveness of an anticonvulsant drug.
• Antidepressants. Taking ginkgo with certain antidepressants, such as fluoxetine (Prozac, Sarafem) and imipramine (Tofranil), might decrease their effectiveness.
• Certain statins. Taking ginkgo with simvastatin (Zocor) might reduce the drug's effects. Ginkgo also appears to reduce the effects of atorvastatin (Lipitor).
• Diabetes drugs. Ginkgo might alter your response to these drugs.
• Ibuprofen. It's possible that combining ginkgo with ibuprofen (Advil, Motrin IB, others) might increase your risk of bleeding.