Horse chestnut is primarily used for its effects on the peripheral vascular system. The tree is grown primarily for ornamental purposes today, and can be found throughout towns and parks in the temperate regions of the United States. The tree itself produces copious amounts of its ‘fruit,’ which resembles small, prickly brown eggs. Within the fruit are the seeds, or nuts, which possess medicinal value.
As early as the 1800’s, European physicians discovered the use of seed extracts derived from the horse chestnut tree; being used for treating disorders characterized by insufficient veins and poor circulation. The use of horse chestnut is stilly highly regarded in Europe, where German physicians have made it the 3rd most prescribed herbal medicine.
While the active constituents of horse chestnut may be derived from the seed, bark, flowers, and leaves, those used for nutritional supplementation purposes are extracts derived from seeds. The active ingredient of this herb is known as aescin, or sometimes spelled as escin.  The raw parts of horse chestnut are considered quite toxic, however. Before processing, when the toxic hydroxycoumarin esculin is present, oral ingestion can be lethal.  No part of the plant should be used raw as it can result in poisoning. 
Horse Chestnut Uses
Aescin has the ability to decrease venous permeability, thereby decreasing swelling as a result of incompetent veins. Laboratory studies have shown that aescin can cause constriction of the veins and reduce the permeability of capillaries.  Because of these properties, horse chestnut is indicated for varicose veins and venous insufficiency, hemorrhoids, and phlebitis - a type of venous inflammation.
These venous-specific properties are the reason for horse chestnut’s inclusion into several cosmetic formulations.  Additionally, horse chestnut extract appears to work as a weak diuretic agent, further enhancing its effects as a swelling reducer. 
Other uses of horse chestnut, not entirely related to its venous-specific effects, include diarrhea, fever, and enlarged prostate glands. Horse chestnut bark has been used for malaria and dysentery while the leaf has been used for treating eczema, menstrual cramping, arthritis, cough, and tissue swelling from injury.
For treatment of venous insufficiency, extract in 300 - milligram capsules can be taken twice per day. The extract should be standardized to contain 50 milligrams of aescin. [6, 7]
Horse Chestnut Side effects:
Taken in the processed form, horse chestnut is generally well tolerated. Some reported side effects, however, include dizziness, nausea, headaches, and itchiness. 
There are also documented reports of gastrointestinal irritation and kidney toxicity from taking this herb; however the form is not specified.  Other reported side effects include; increased risk of bleeding or bruising, allergy to pollen, and allergic hypersensitivy in those prone to latex allergy. [9-11] Contact allergic dermatitis, liver damage, and complications arising from intravenous administration, may occur as well. [12-14]
Horse Chestnut General interactions (supplement, herb, food, lab):
There are no known interactions with foods or lab tests when using horse chestnut extract. Because of the unsafe nature of unprocessed or raw horse chestnut products, it should be avoided in pregnancy and lactation. Otherwise, raw horse chestnut products should never be used.
Herbs or supplements with possible anticoagulant effects should be used with caution when taken in conjunction with horse chestnut; there is possibility that increased bleeding risk may occur.
Horse Chestnut Drug interactions:
Similarly, drugs with anticoagulant or antiplatelet effects should not be used with horse chestnut because of the possibility of additive effects when combined. This grouping also includes aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), as well as standard blood thinning medications.
- Digestive disorders: horse chestnut may further irritate the intestines and should not be used in inflammatory digestive conditions.
- Liver disease: caution should be exercised when using horse chestnut; there is one case report of liver damage associated with this herb. 
- Latex allergy: those that have a known latex allergy should avoid the use of horse chestnut as cross-sensitivity may be an issue.
- Kidney disease: similar to liver disease, caution should be exercised when using this herb in conditions of kidney impairment, kidney toxicity has been reported.
1 Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
2 Ellenhorn MJ, et al. Ellenhorn’s Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
3 Martindale W. Martindale the Extra Pharmacopoeia. Pharmaceutical Press, 1999.
4 Dr. Duke’s Phytochemical and Ethnobotanical Databases. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml.
5 Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996. 4 Ibid
6 Pittler MH, Ernst E. Horse-chestnut seed extract for chronic venous insufficiency. A criteria-based systematic review. Arch Dermatol 1998;134:1356-60.
7 Diehm C, Trampisch HJ, Lange S, Schmidt C. Comparison of leg compression stocking and oral horse-chestnut seed extract in patients with chronic venous insufficiency. Lancet 1996;347:292-4.
8 Pittler MH, Ernst E. Horse chestnut seed extract for chronic venous insufficiency (Cochrane Review). In: The Cochrane Library, Issue 3, 2004. Chichester, UK: John Wiley & Sons, Ltd. 5 Ibid
9 Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
10 Popp W, Horak F, Jager S, et al. Horse chestnut (Aesculus hippocastanum) pollen: a frequent cause of allergic sensitization in urban children. Allergy 1992;47:380-3.
11 Diaz-Perales A, Collada C, Blanco C, et al. Cross-reactions in the latex-fruit syndrome: A relevant role of chitinases but not of complex asparagine-linked glycans. J Allergy Clin Immunol 1999;104:681-7.
12 Comaish JS, Kersey PJ. Contact dermatitis to extract of horse chestnut (esculin). Contact Dermatitis 1980;6:150-1.
13 Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.
14 Robbers JE, Tyler VE. Tyler’s Herbs of Choice: The Therapeutic Use of Phytomedicinals. New York, NY: The Haworth Herbal Press, 1999. 5 Ibid