Yarrow

Yarrow, a member of the daisy family (Asteraceae), has one of the oldest documentations of human use throughout a variety of cultures worldwide. Many of these cultures share common threads of yarrow being used to heal wounds and treat inflammation, gastrointestinal distress, and menstrual concerns. The common name “yarrow” is sometimes used for a group of plants including other species of Achillea, so attention to full scientific names is advised. The genus name (Achillea) originates from Greek mythology: Achilles used yarrow to remedy wounds. Yarrow can be taken internally as a tea, while external applications usually take the form of lotions and ointments. The leaves and flowering tops are the parts most often used medicinally, but there are ethnobotanical records of traditional medicinals employing the entire plant.^[1][2]

The strongest evidence for yarrow exists in topical applications for wound healing and, to some degree, reductions in localized irritations or infections.^{[3][4][5][6][7][8][9][10][11][12]} Though there are some promising clinical studies regarding the use of yarrow (either alone or in combination with other herbs) for menstrual or gastrointestinal distress, among other chronic concerns and conditions, further research should be conducted to confirm these findings.^[13][14]

Since yarrow is a member of the Asteraceae family, anyone with allergies to other plants in that family (e.g., marigolds, ragweed, daisies) has a higher risk of having an allergic reaction to yarrow. Yarrow contains thujone, which is responsible for some of its antibacterial properties, but also runs the risk of neurotoxicity when consumed (at best estimate) in doses greater than 3–7 mg of thujone per day.^[15][1][16] More clinical evidence is required to better understand the safety of consuming thujone-containing products. While skin rashes are the most frequently reported adverse response to yarrow (and are believed to be due to guaianolides), the majority of the few clinical studies have excluded participants who might experience herb-drug interactions, which would reduce the number of reported adverse reactions.^[1]

While it may not have the same degree of mechanistic evidence behind it as some other herbs, the active components found in yarrow may provide some support for its traditional uses.^[1] Yarrow is known to contain the compounds apigenin; luteolin; camphor; borneol; centaureidin; quercetin; 5-hydroxy-3’,4’,6,7-tetramethoxyflavone; thujone; dicaffeoylquinic acid; 1,8-cineole; and chlorogenic acid (among many others).^[1][15][17] The antioxidant, anti-inflammatory, antimicrobial, antispasmodic, estrogenic, pain-reducing, hepatoprotective, and vasodilatory effects of the individual constituents of yarrow are already known, and may explain some of the herb’s purported effects.^[1][15][17] Further mechanistic studies are needed to further understand the biological activity and bioavailability of these components when taken together in the whole herb or in an herbal extraction.