From the Manufacturer:
Horse chestnut, also called buckeye, is a tree native to the Bulkan peninsula. Extract of its seeds, leaves and bark have been used for centuries for a variety of health benefits, but particularly for venous insufficiency, in which veins in the legs do not efficiently return blood to the heart.
Horse chestnut seed contains aescin, a compound believed to help tone vein walls, contributing to improved blood flow. It may also have anti-inflammatory effects and help to stop excessive leakage through walls of the capillaries (tiny vessels that deliver blood to tissues). Studies suggest horse chestnut may promote reduced swelling in legs as effectively as compression stockings; however more research is needed to confirm this effect.
NSI® Horse Chestnut Complex contains 500 mg of horse chestnut extract standardized to 20 percent aescin. It also features 200 mg of calendula, an herbal extract containing triterpenoids, which have anti-inflammatory properties, and antioxidant flavonoids. Calendula may also have immune-stimulating effects.