Over 100 species of Achillea are known, many of which are cultivated or used medicinally. The genus originated in Eurasia, but a few species, including A. millefolium, have spread to other continents. Several European and North American subspecies of yarrow form a polyploid complex with considerable variation in both morphology and chemical content, even within subspecies. Yarrow has been used medicinally in Europe for millennia for many purposes, notably to treat respiratory diseases and gastrointestinal complaints, to alleviate cramps, and to stop bleeding and improve wound healing. Like many other plants used for febrile illnesses, hot yarrow tea is believed to alleviate symptoms by inducing sweating. Fresh yarrow poultices are used topically on bleeding wounds, and yarrow preparations have traditionally been used for internal bleeding. Interestingly, the North American yarrow is widely used in Native American traditions for similar purposes.

In vitro and animal studies demonstrate that yarrow has antibacterial, antioxidant, antispasmodic, liver-protective, antianxiety, and antiulcer activities. It has been observed (by Dr. Jim Duke and others) that if multiple cultures independently value a plant for similar uses, it is especially likely to be effective. It is therefore surprising that no readily locatable human studies have been conducted on yarrow. The plant certainly merits far more research effort than it has received to date. The German Commission E rates yarrow positively to treat dyspepsia and stimulate appetite, based largely on human experience. Yarrow appears to be quite safe in animal studies, even when consumed over very long periods. Very large doses (56 times the human dose) in pregnant rats cause no maternal toxicity, contraceptive effect, fetal loss, or birth defects; however, when given during a specific period of pregnancy, they may reduce fetal weight and increase placental weight relative to controls. Very high doses also reduce sperm counts in male rodents.

Selected References

Boswell-Ruys, C. L., H. E. Ritchie, and P. D. Brown-Woodman. 2003. Preliminary screening study of reproductive outcomes after exposure to yarrow in the pregnant rat. Birth Defects Res. B Dev. Reprod. Toxicol. 68:416-420.

Cavalcanti, A. M., C. H. Baggio, C. S. Freitas, L. Rieck, R. S. de Sousa, J. E. Da Silva-Santos, S. Mesia-Vela, and M. C. Marques. 2006. Safety and antiulcer efficacy studies of Achillea millefolium L. after chronic treatment in Wistar rats. J. Ethnopharmacol. 107:277-284.

Ehrendorfer, F. 1973. New chromosome numbers and remarks on the Achillea millefolium polyploid complex in North America. Österr. Bot. Z. 122:133-143.

Gervais, C. 1977. Cytological investigation of the Achillea millefolium complex (Compositae) in Quebec. Canad. J. Bot. 55:796-808.

Guédon, D., P. Abbe, and J. L. Lamaison. 1993. Leaf and flower head flavonoids of Achillea millefolium L. subspecies. Biochem. Syst. Ecol. 21:607-611.

Guo, Y. P., J. Saukel, R. Mittermayr, and F. Ehrendorfer. 2005. AFLP analyses demonstrate genetic divergence, hybridization, and multiple polyploidization in the evolution of Achillea (Asteraceae-Anthemideae). New Phytol. 166:273-289.

Kokkalou, E., S. Kokkini, and E. Hanlidou. 1992. Volatile constituents of Achillea millefolium in relation to their infraspecific variation. Biochem. Syst. Ecol. 20:665-670.

Molina-Hernandez, M., N. P. Tellez-Alcantara, M. A. Diaz, J. Perez Garcia, J. I. Olivera Lopez, and M. T. Jaramillo. 2004. Anticonflict actions of aqueous extracts of flowers of Achillea millefolium L. vary according to the estrous cycle phases in Wistar rats. Phytother. Res. 18:915-920.

Orav, A., E. Arak, and A. Raal. 2006. Phytochemical analysis of the essential oil of Achillea millefolium L. from various European countries. Nat. Prod. Res. 20:1082-1088.

Richardson, I. B. K. 1976. Achillea. Pp. 159-165 in: T. G. Tutin et al., eds. Flora Europaea, vol. 4. Cambridge University Press, Cambridge.

Yaeesh, S., Q. Jamal, A. U. Khan, and A. K. Gilani. 2006. Studies on hepatoprotective, antispasmodic and calcium antagonist activities of the aqueous-methanol extract of Achillea millefolium. Phytother. Res. 20:546-551.