The horse chestnut tree is widely cultivated for its bright white, yellow, or red flower clusters. Closely related to the Ohio buckeye, this tree produces large seeds known as horse chestnuts. A superstition in many parts of Europe suggests that carrying these seeds in your pocket will ward off rheumatism. More serious medical uses date back to nineteenth-century France, where extracts were used to treat hemorrhoids.

Serious German research of this herb began in the 1960s and ultimately led to the approval of a horse chestnut extract for vein diseases of the legs. Horse chestnut is the third most common single-herb product sold in Germany, after ginkgo and St. John's wort. In Japan, an injectable form of horse chestnut is widely used to reduce inflammation after surgery or injury; however, it is not available in the United States, and it may present safety risks.

The active ingredients in horse chestnut appear to be a group of chemicals called saponins, of which aescin is considered the most important. Aescin appears to reduce swelling and inflammation.1,31It is not exactly clear how aescin might work, but theories include "sealing" leaking capillaries, improving the elastic strength of veins, preventing the release of enzymes (known as glycosaminoglycan hydrolases) that break down collagen and open holes in capillary walls, decreasing inflammation, and blocking other various physiological events that lead to vein damage.2,3,31

Horse chestnut is most often used as a treatment for venous insufficiency. This is a condition associated with varicose veins, when the blood pools in the veins of the leg and causes aching, swelling, and a sense of heaviness. While horse chestnut appears to reduce these symptoms, no studies have evaluated whether it can make visible varicose veins disappear, or prevent new ones from developing.

Because hemorrhoids are actually a form of varicose veins, horse chestnut is used for them as well, and one double-blind, placebo-controlledstudy suggests that it may be effective.31

Horse chestnut may also help improve sperm counts in men suffering from infertility due to varicocele, a type of varicose veins that affects the testicles.33

Another double-blind study found that a topically applied gel made from horse chestnut may be helpful for bruises.5 Oral horse chestnut has also been proposed for minor injuries and surgery,4,31 but published studies on this potential use were not double-blind. (For reasons why double-blind studies are important, see Why Does This Database Rely on Double-blind Studies?)

Finally, horse chestnut is sometimes used along with conventional treatment in cases where the veins of the lower legs become seriously inflamed (called phlebitis). Note: Phlebitis is potentially dangerous and requires a doctor's supervision.