From periwinkle, a memory aid

Vinpocetine, first discovered in the 1960s, is produced in the lab by chemically altering vincamine, a compound from the Vinca minor periwinkle plant. In some countries, such as Germany, it’s available only by prescription, but in the United States it’s sold as a supplement for enhancing memory and focus.

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Uses: Vinpocetine has been used for decades to treat Alzheimer’s disease, dementia and stroke patients in Europe, Japan, Mexico and sometimes the U.S. It’s also used to prevent motion sickness and -- increasingly in this country -- to improve cognitive functioning in healthy adults.

Dose: Usually, 5 to 10 milligrams a day, taken with meals to improve absorption.

Precautions: The supplement may lower blood pressure and delay clotting in people with bleeding disorders or on blood-thinning medications. Although side effects are not common, according to existing studies, vinpocetine can cause headaches, stomachaches, flushing and nausea.

Research: Most of the studies on vinpocetine have been short-term, small-scale investigations. Research has shown that the supplement does improve blood circulation in the brain and may speed the healing of eye and ear injuries. Studies on Alzheimer’s patients, however, have failed to show any benefit from vinpocetine, and studies on ischemic stroke patients have been too limited to produce conclusive results.

Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.

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-- Elena Conis