

The parts used are the fruits (conkers) and the young leaves. The conkers contain saponins and coumarins. Preparations of horse chestnut can be made for both internal and external applications. It is perfectly safe to use externally on unbroken skin, but needs to be used under professional supervision if taken internally as there can be quite serious side effects from taking too high a dose.
Primary use is as a venous tonic. Used both internally and topically for varicose insufficiency, varicose, eczema, varicose veins, piles. It should be used cautiously with blood thinning agents. Probably OK with aspirin, but don't use if taking warfarin. Also, do not use if there is any renal or hepatic impairment.
Coumarin (aesculetin), Saponins (aescin), tannins, flavonoids.