Horse chestnut trees are native to the Balkan Peninsula (which includes such countries as Albania, Bulgaria, Greece, Romania, and Serbia), but are grown worldwide.
Historically, horse chestnut seed extract was used for joint pain, bladder and gastrointestinal problems, fever, and leg cramps.
Today, people use horse chestnut extract as a dietary supplement for chronic venous insufficiency (when the veins of the lower leg are unable to send blood back toward the heart), hemorrhoids, and swelling after surgery. Preparations made from the tree’s bark are applied to skin sores.
Usable parts of the plant include the seed, bark, and leaf, but seed extracts are most common.
A 2012 systematic review of 17 studies published between 1976 and 2002 suggested that horse chestnut seed extract can improve leg pain, swelling, and itching in people with chronic venous insufficiency when taken for a short time. Results from one of these studies suggested that horse chestnut seed extract may be as effective as wearing compression stockings.
Preliminary evidence from one Chinese study suggested that escin, the main ingredient in horse chestnut, may help restore fertility in some men. However, since all the men in the study also received other supplements and drugs, it’s unclear whether the improvement was due to this compound alone or the combination approach.
The unprocessed seeds, leaves, bark, and flowers of horse chestnut contain esculin, which is poisonous and may increase the risk of bleeding. (Escin, on the other hand, is a different compound and is considered to be safe.)
Properly processing horse chestnut seed extract removes esculin. The processed extract is considered generally safe when used for short periods of time. However, the extract can cause some side effects, including itching, nausea, gastrointestinal upset, muscle spasm, or headache.