Yarrow

Achillea millefolium L. sits in Asteraceae, tribe Anthemideae, alongside chamomile and tansy. Linnaeus published it in Species Plantarum (1753, vol. 2, p. 899). NCBI Taxonomy files it as taxon 13329 and, tellingly, nests it inside a node called the “Achillea millefolium complex.” It is a rhizomatous perennial, 6 to 65 cm or more tall, often forming clonal mats. Leaves are oblong to lanceolate in outline and one- to two-pinnately dissected into narrow lobes that often sit in several planes—hence thousand-leaf, milfoil, and the German Schafgarbe. Flora of North America records ten to more than a hundred small heads per stem, packed into flat-topped (corymbiform) arrays. Each head has (3–)5–8 short ray florets, usually white but sometimes pink to deep purple, surrounding 10–20 tiny disc florets. The ray blades are only 1.5–3 mm long. From a distance the cluster reads as one flower; up close it is a crowd of miniature daisies.

The range is circumboreal and then some. FNA lists the species in every Canadian province and territory, Greenland, nearly every US state, Mexico, and Eurasia, from sea level to 3,600 m, in pastures, roadsides, dunes, waste ground, and salty or clayey soils. Whether North American yarrow is native, introduced, or both has been argued for decades; at least 58 names have been applied to North American specimens, including A. lanulosa and A. borealis. FNA follows the view that this is one Northern Hemisphere polyploid complex of native and introduced plants that have hybridised, with chromosome counts of 2n = 18, 27, 36, 45, 54, 63, and 72. Other workers keep the native western tetraploids and hexaploids as A. borealis. Ramsey (PNAS 2011) used coastal Californian populations to show that hexaploids had a fivefold fitness advantage over tetraploids on sand dunes, and that first-generation neohexaploids already carried a 70% advantage. Genome duplication itself was doing ecological work.

In Europe the same complexity is split into named species. Ehrendorfer’s mid-century cytology recognised diploid, tetraploid, hexaploid, and octoploid levels in the aggregate (Achillea millefolium agg.). Hexaploids were treated as A. millefolium in the strict sense, octoploids as A. pannonica, and most of the variable tetraploids as A. collina; A. pratensis Saukel & Länger is a later-described tetraploid of mesic meadows (Danihelka and Rotreklová, Preslia 2001). Chromosome number matters to a pharmacist because it tracks chemistry. The EMA assessment report, citing WHO, puts it this way: diploid and tetraploid plants contain proazulene sesquiterpenes, including achillicin, and their oil can carry up to about 25% chamazulene; hexaploids are azulene-free; octoploids are dominated by oxygenated monoterpenes. A. collina is the classic proazulene-rich tetraploid. Later crossing work found that proazulene production behaves as a recessive, population-level trait, not a perfect species badge.

The European Pharmacopoeia drug is the dried flowering tops, with at least 2 ml/kg essential oil and at least 0.02% proazulenes expressed as chamazulene. EMA lists 3–4% tannins; 0.3–1.4% volatile oil (linalool, borneol, camphor, β-caryophyllene, 1,8-cineole); guaianolide sesquiterpene lactones (achillicin, achillin, leucodin); flavonoids (apigenin, luteolin, rutin); caffeic acid and dicaffeoylquinic acids; and small bases such as achilleine. Chamazulene (PubChem CID 10719, C14H16) is essentially absent from the living plant. Heat and water during steam distillation convert colourless achillicin, via chamazulenic acid, into the blue azulene—which is why some yarrow oils come off the still ink-blue and others do not. Thujone is the other chemotype story. Orav and colleagues found 0–26.6% α-thujone and 0–11% β-thujone across 19 European oil samples, with means near 2%; most other studies found little or none. EMA concluded that thujone is a minor component and calculated a worst case of no more than about 1.5 mg a day from maximum monograph tea doses.

The genus name is a myth. Pliny the Elder’s Natural History (book 25, chapter 19) says Achilles, pupil of the centaur Chiron, discovered a wound-healing plant called achilleos and cured Telephus with it. In the same passage Pliny admits other authorities credited copper rust scraped from Achilles’ spear, and that Romans called the plant millefolium. The Iliad itself does not name yarrow, and the Telephus episode is a later literary layer. Linnaeus kept the hero for the genus anyway. The pseudo-Apuleius herbal tradition carried the plant as millefolium with “militaris” among its synonyms, and the uses stayed remarkably constant: wounds from iron weapons, nosebleeds, bleeding haemorrhoids, heavy periods. Yarrow stalks also have a separate, non-medical life. The classical method of consulting the Chinese I Ching uses fifty dried stalks, traditionally Achillea, divided and counted off in fours to build each line of a hexagram.

The prehistoric claims are where skepticism earns its keep. In 1975 Ralph Solecki reported in Science that pollen clumps beside the Shanidar IV Neanderthal in Iraq showed a burial on a bed of flowers; Arlette Leroi-Gourhan’s identifications included Achillea-type pollen. The “first flower people” became a textbook image. Sommer (Cambridge Archaeological Journal 1999) pointed out that Persian jirds, burrowing rodents present at the site, cache flower heads in their tunnels in quantities large enough to explain the pollen. Hunt, Pomeroy, Reynolds, Tilby, and Barker (Journal of Archaeological Science 2023) re-examined the palynology and concluded that at least some clumps were most likely left by nesting solitary bees. The burial is real; the bouquet probably is not. The El Sidrón evidence is firmer but narrower. Hardy and colleagues (Naturwissenschaften 2012) analysed dental calculus from five Neanderthals in northern Spain and reported evidence that one individual had ingested yarrow and chamomile—bitter plants of little food value, which the authors read as possible self-medication. That is one tooth deposit and an inference, not a pharmacopoeia.

In North America, Daniel Moerman’s Native American Ethnobotany Database records yarrow from the Abenaki, who gave infusions to children with colds, to the Cheyenne, who packed crushed leaves into the nose for nosebleeds; the Cherokee used it for haemorrhage and restful sleep, the Blackfoot for sore throats and to ease labour, the Bella Coola as a burn poultice. Applequist and Moerman (Economic Botany 2011) called it “one of the most widely used medicinal plants in the world,” mainly for wounds, digestive problems, respiratory infections, and skin conditions, and asked whether it was a neglected panacea. In Germany, Commission E (1990) approved the herb internally for loss of appetite and mild spasmodic dyspeptic complaints, and in sitz baths for cramp-like pelvic pain in women; the Madaus handbook of 1938 already listed it for dysmenorrhoea. EMA’s HMPC turned that heritage into traditional-use monographs for the flower (2011) and the herb (2011, revised 2020), and opened a call for data for a further periodic review in 2026.

EMA does not require a mechanism for traditional-use products; both monographs say pharmacodynamic data are “not required.” The herb assessment notes laboratory evidence of antibacterial, spasmolytic, and anti-inflammatory effects. The plausible story runs like this. Bitter sesquiterpene lactones and aromatic oil fit the old “bitter aromatic” appetite role. Apigenin, luteolin, and their glycosides were identified as spasmolytic flavonoids across the whole A. millefolium complex as early as 1968, which is the logic behind the cramp indications. Tannins are astringent, which fits the wound and bleeding folklore. Chamazulene is the compound marketers point to, but only some chemotypes make its precursors, and a water infusion carries little of the oil. None of that is a dose-response curve in a human gut or uterus.

The same chemistry that makes yarrow interesting makes it allergenic. Sesquiterpene lactones carrying an α-methylene-γ-butyrolactone group are the classic Asteraceae contact allergens. Hausen, Breuer, Weglewski, and Rücker (Contact Dermatitis 1991) identified α-peroxyachifolid, a guaianolide peroxide, as yarrow’s main sensitiser in guinea-pig experiments. The menstrual folklore also cuts both ways. Yarrow was called an emmenagogue and abortifacient in German folk sources and elsewhere, yet the one rat study usually cited (Boswell-Ruys, Ritchie, and Brown-Woodman, Birth Defects Research B 2003) found no increase in implantation loss or malformations at 56 times the human dose—only lower fetal weight and heavier placentas, with alcohol in the extract as a possible contributor. Mechanism here is mostly inference stacked on folklore.

The regulatory reading is narrow. Under EMA’s traditional-use rules, yarrow herb and yarrow flower may be registered for four uses: temporary loss of appetite; symptomatic relief of mild, spasmodic gastrointestinal complaints including bloating and flatulence; minor spasm associated with menstrual periods; and, applied to the skin, small superficial wounds. “Traditional” means at least 30 years of medicinal use, 15 of them in the EU, plausible efficacy, and a self-care indication. It does not mean a trial showed benefit. The herb assessment states that no clinical study of oral yarrow herb was available. The flower summary is blunter: no clinical studies with yarrow flower medicines are available.

Menstrual cramps have the most-cited trial. Jenabi and Fereidoony (Journal of Pediatric and Adolescent Gynecology 2015) randomised 96 female university students in western Iran with primary dysmenorrhoea to yarrow flower-head tea or a starch placebo tea; 91 were analysed. The yarrow group drank 4 g in 300 ml of hot water three times a day for the first three days of two cycles. Pain on a visual analogue scale fell more with yarrow at one and two months (P = .001 and P < .0001), and no side effects were reported. It is one small, single-site trial analysed with simple t-tests, and its dose—about 12 g of flower a day—is well above EMA’s flower posology of 1–2 g two or three times daily. Encouraging, not established. It does not tell you how yarrow compares with an ordinary anti-inflammatory painkiller.

Two other trials are interesting and isolated. Ayoobi and colleagues (Phytomedicine 2019) randomised 75 people with relapsing-remitting multiple sclerosis at one Iranian centre to placebo or 250 or 500 mg a day of an aqueous yarrow extract as add-on therapy for a year; 65 completed. Both doses lowered the annualised relapse rate, and the higher dose reduced MRI lesion-volume change and improved some disability and cognitive scores. Twenty-five patients per arm, many secondary outcomes, and no replication: that is a hypothesis for a larger trial, not a reason to change an MS regimen. On the skin, Hajhashemi and colleagues (Journal of Maternal-Fetal and Neonatal Medicine 2018) compared a 5% yarrow extract ointment, a St John’s wort ointment, placebo ointment, and no treatment on episiotomy wounds in 140 first-time mothers. Pain, redness, oedema, and bruising were lower with both herbal ointments; wound breakdown and discharge did not differ. EMA noted that only 32 women used the yarrow ointment and that the product matches no monograph preparation.

Beyond those, the claims outrun the data. Yarrow is sold for colds and fevers (the old “sweat it out” diaphoretic use), blood pressure, liver support, anxiety, ulcers, haemorrhoids, and cancer. Applequist and Moerman found preclinical signals for anti-inflammatory, anti-ulcer, hepatoprotective, and anxiolytic activity and argued that human trials should be funded—precisely because they had not been done. A tincture is not a styptic for a cut that will not stop bleeding, and a tea is not a treatment for hypertension, infection, or cancer. Folklore that agrees across continents is a reason to study a plant. It is not an outcome measure.

EMA herb monograph (Millefolii herba, revision 1), for adolescents over 12, adults, and the elderly. For loss of appetite and mild spasmodic digestive complaints: herbal tea of 1.5–4 g comminuted herb in 150–250 ml boiling water, three or four times daily between meals. Alternatives in the same file: expressed juice of fresh herb, 5–10 ml two or three times daily; liquid extract (1:1, ethanol 25%), 2–4 ml three times daily; tincture (1:5, ethanol 45%), 2–4 ml three times daily; tincture (1:5, ethanol 31.5%), 4.3 ml four times daily; or, for digestive complaints only, 334 mg of an aqueous dry extract (DER 6–9:1) three or four times daily. For appetite, liquid preparations are taken 30 minutes before meals. See a doctor or qualified practitioner if symptoms last more than two weeks.

For minor menstrual cramps the herb monograph lowers the dose: 1–2 g in 250 ml boiling water two or three times daily, or 250 mg of an aqueous dry extract (DER 5–10:1) two or three times daily. For small superficial wounds: an infusion of 3–4 g in 250 ml boiling water, applied two or three times daily as an impregnated dressing. Both carry a one-week limit before seeing a clinician, and signs of skin infection mean medical advice now. The flower monograph (Millefolii flos) is parallel but lighter: tea of 1.5–2 g in 250 ml twice daily for appetite and digestion; a wine-and-ethanol liquid extract, 10–20 drops two or three times daily, for digestive spasm; 1–2 g tea two or three times daily for menstrual cramps; and 1.5 g in 250 ml water as a wound dressing.

Outside licensed EU products, yarrow arrives as loose dried herb, tea blends, tinctures of unstated strength, capsules, creams, and essential oil. Plant part, chemotype, and ploidy are almost never declared. A proazulene-rich tetraploid and an azulene-free hexaploid can both be sold as Achillea millefolium. Pharmacopoeial herb must reach 0.02% proazulenes as chamazulene and 2 ml/kg oil; a roadside harvest has no known chemotype, dose, or spray history. If you want the object EMA assessed, look for a product that names the plant part, the preparation, and a strength that matches the monograph.

Blue yarrow essential oil is not tea. It concentrates the volatile fraction, including whatever camphor, 1,8-cineole, or thujone a given chemotype carries, and no EMA monograph covers it for internal use. Do not drink it, do not give it to children, and do not put it on skin undiluted—skin is where yarrow allergy shows up. Fresh leaves pressed on a scrape are the oldest preparation of all; they are also a direct route to contact dermatitis in sensitised people.