Horse chestnut may help treat chronic venous insufficiency, but its long-term effects are not known.
Horse chestnut is a seed extract. One of its active components is aescin, which may reduce inflammation and increase vein tone. It also reduces the release of enzymes that typically increase with chronic vein diseases. Other compounds in horse chestnut generally improve blood vessel tone. In some studies, horse chestnut extract was effective against chronic venous insufficiency.
A compound called aesculetin may act as an anticoagulant and blood thinner, and is therefore often excluded from over-the-counter horse chestnut products.