Yarrow:

http://www.vitacost.com/science/hn/Herb/Yarrow.htm

A number of chemicals may contribute to yarrow’s actions. The volatile oil, which is rich in sesquiterpene lactones, and alkamides has been found to have anti-inflammatory properties in test tube studies.3 & 4

Animal studies have shown this herb can reduce smooth muscle spasms, which might further explain its usefulness in gastrointestinal conditions.5 The alkaloid obtained from yarrow, known as achilletin, reportedly stops bleeding in animals.6 No human clinical studies have confirmed the traditional uses of yarrow.

How much is usually taken?

The German Commission E monograph suggests approximately 1 teaspoon (4.5 grams) of yarrow daily or 3 teaspoons (15 ml) of the fresh pressed juice.7 A tea can be prepared by steeping 1–2 teaspoons (5–10 grams) of yarrow in 1 cup (250 ml) boiling water for ten to fifteen minutes. Three cups (750 ml) a day can be taken. A tincture, 1/2–3/4 teaspoon (3–4 ml) three times per day, can be taken. The tea, or cloths dipped in the tea, can be used topically as needed for minor skin injuries.

Are there any side effects or interactions?

People who take yarrow may occasionally develop an allergy or rash.8 Yarrow might increase sensitivity to sunlight. Yarrow should not be used to treat large, deep, or infected wounds, all of which require medical attention. Yarrow is not recommended during pregnancy or breast-feeding.9

At the time of writing, there were no well-known drug interactions with yarrow.

References

1. Castleman M. The Healing Herbs. New York, Bantam Books, 1991, 550–4.

2. Castleman M. The Healing Herbs. New York, Bantam Books, 1991, 550–4.

3. Zitterl-Eglseer K, Jurenitsch J, Korhammer S, et al. Sesquiterpene lactones of Achillea setacea with antiphlogistic activity. Planta Med 1991;57:444–6.

4. Muller-Jakic B, Breu W, Probstle A, et al. In vitro inhibition of cyclooxygenase and 5-lipoxygenase by alkamides from Echinacea and Achillea species. Planta Med 1994;60:37–40.

5. Tewari JP, Srivastava MC, Bajpai JL. Pharmacologic studies of Achillea millefolium Linn. Indian J Med Sci 1994;28:331–6.

6. Duke JA. CRC Handbook of Medicinal Herbs. Boca Raton, FL: CRC Press, 1985, 10–1.

7. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 233–4.

8. McGuffin M, Hobbs C, Upton R, Goldberg A. American Herbal Products Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997, 3.

9. McGuffin M, Hobbs C, Upton R, Goldberg A (eds). American Herbal Products Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997, 3.

http://elements.eyesis.co.nz/article_archive/yarrow.html

Properties: Anti-inflammatory, antipyretic, antirheumatic, antiseptic, antispasmodic, astringent, carminative, cholagogue, cicatrisant, diaphoretic, digestive, expectorant, febrifuge, haemostatic, hypotensive, stimulant, stomachic, tonic

The herb can be used internally for arthritis, diarrhoea, fevers, hypertension, menstrual problems, menopause and rheumatism. Externally the herb can be used for eye inflammation, haemorrhoids, nosebleeds (hence one of its folk names, "nosebleed"), sores and to stop bleeding when a poultice is placed on wounds or shaving cuts.

http://www.naturesalternatives.com/herbs/yarrow.html

Yarrow is one of the best diaphoretic herbs and is a standard remedy for aiding the body to deal with fevers. It lowers blood pressure due to a dilation of the peripheral vessels, stimulates digestion and tones the blood vessels. As a urinary antiseptic it is indicated in infections such as cystitis. Preparations of yarrow flower have been shown to stimulate the gastric juices, this would account for yarrows effectiveness as a tonic, with improved digestion of foods, which is due to the presence of bitter substances in the blossoms. Test tube studies have shown yarrow to possess antibiotic properties.

http://healthyherbs.about.com/library/weekly/aa061998.htm

Yarrows history and reputation dates back 3000 years ago to the Trojan war. Achilles packed yarrow on soldiers wounds to stop the bleeding. It was also used extensively during the Amercian Civil War.

Yarrow helps stop bleeding both externally and internally. For an external application, fresh yarrow seems to be best. If you are bleeding internally, you need to seek emergency medical help, do not treat yourself. If can help however, in an emergency and you are stranded somewhere bleeding internally. Yarrows anti-inflamatory agent, azulene can vary from plant to plant.[5]

As a diaphoretic (makes you sweat) it apparently does the job well. As Howie Brountstein writes, "yarrow tincture is a sauna in a bottle".

Handling yarrow may cause contact dermatitis. According to research the "compounds alpha- peroxyachifolid (1) and beta-peroxyisoachifolid (2) are proposed. 1 is responsible for the allergic contact dermatitis caused by yarrow."