Horse chestnuts are not safe to eat. They contain toxic compounds, particularly aescin and other saponins, which can cause serious gastrointestinal distress and other toxic symptoms in humans if consumed. These nuts are different from edible sweet chestnuts and can be easily mistaken for them because of their similar appearance. Eating horse chestnuts can lead to nausea, vomiting, colic, and in some cases more severe toxic effects. Therefore, horse chestnuts should never be eaten raw or cooked like traditional edible chestnuts.
Horse chestnuts are also toxic to many animals including horses, cattle, and sheep. Despite their toxicity, extracts from horse chestnuts are used medicinally in controlled forms to treat conditions like chronic venous insufficiency, but the raw nuts themselves are poisonous.
In summary, horse chestnuts are toxic and not edible for humans or most animals. Only sweet chestnuts from the Castanea genus are safe to eat.
