Yarrow

Traditionally, yarrow was used as a styptic and vulnerary, and was especially useful in times of war by the soldiers. Some of its common names reflect this use very well such as “Soldiers wound wort”, and “Knights milfoil”. The famous herbalist Gerard suggests that yarrow was used by Achilles to stanch the bleeding of his soldiers ^{35,12Reference 35A Modern Herbal (Grieve M) · 1931YarrowView study →Reference 12Agar OT et al. · 2015In vitroComparative studies on phenolic composition, antioxidant, wound healing and cytotoxic activities of selected Achillea L. species growing in Turkey — [in vitro]View study →}. This may be why the herb’s botanical name is Achillea millefolium. He also suggested its use for headaches, to stop nosebleeds, and for toothaches ^{36Reference 36Battaglia S · 2003The Complete Guide to Aromatherapy (2nd ed.)}.

Culpeper suggested it is “drying and binding” and suggested a poultice of yarrow for treating piles, and an ointment of the leaves for wounds ^{36Reference 36Battaglia S · 2003The Complete Guide to Aromatherapy (2nd ed.)}.

In the 17th century its leaves were used in salads despite its highly bitter taste ^{35Reference 35A Modern Herbal (Grieve M) · 1931YarrowView study →}.

A wash was used to prevent baldness and treat bleeding piles by making a strong decoction of the whole plant ^{35Reference 35A Modern Herbal (Grieve M) · 1931YarrowView study →}.

Yarrow is considered to be cooling and drying. It stimulates the liver and regulates the flow of Qi. It’s generally used for inflammatory and digestive conditions and releasing stagnant Qi ^{36Reference 36Battaglia S · 2003The Complete Guide to Aromatherapy (2nd ed.)}.

Yarrow’s best-replicated activity is relaxation of smooth muscle. A crude aqueous-methanol extract relaxed spontaneous and K⁺-induced contractions in isolated rabbit jejunum and shifted calcium concentration-response curves rightward, behaving like the calcium-channel blocker verapamil ^{8Reference 8Yaeesh S et al. · 2006AnimalStudies on hepatoprotective, antispasmodic and calcium antagonist activities of the aqueous-methanol extract of Achillea millefolium — [mouse in vivo]View study →}. A hydroalcoholic extract likewise relaxed acetylcholine- and KCl-induced contractions in rat ileum, an effect not blocked by propranolol or the nitric-oxide-synthase inhibitor L-NAME, pointing to a direct musculotropic (calcium-antagonist) mechanism ^{9Reference 9Moradi MT et al. · 2013AnimalAntispasmodic effects of yarrow (Achillea millefolium L.) extract in the isolated ileum of rat — [rat in vivo]View study →}. In guinea-pig trachea the extract acted partly through muscarinic-receptor inhibition ^{10Reference 10Feizpour A et al. · 2013In vitroThe effect of hydro-ethanolic extract of Achillea millefolium on muscarinic receptors of guinea pig tracheal smooth muscle — [in vitro]View study →}. The flavonoid fraction appears to carry much of this antispasmodic activity ^{32Reference 32Benedek B · 2007ReviewAchillea millefolium L. s.l. revisited: recent findings confirm the traditional use — [review]View study →}. All evidence is in vitro/ex vivo — no human trial of yarrow for spasm or colic exists.

Gap: No human data; the effective doses relaxed isolated tissue at concentrations not clearly reached by drinking the herb.

Yarrow’s flagship traditional use is as a styptic and vulnerary, and it has the herb’s clearest human evidence. In a double-blind trial of 140 primiparous women, an A. millefolium ointment reduced episiotomy pain, redness, oedema and ecchymosis versus placebo and non-intervention, though it did not change wound discharge or dehiscence ^{3Reference 3Hajhashemi M et al. · 2018RCTThe effect of Achillea millefolium and Hypericum perforatum ointments on episiotomy wound healing in primiparous women — [double-blind randomised]View study →}. In vitro, yarrow extracts promote fibroblast activity and wound closure and are rich in the antioxidant phenolics thought to support tissue repair ^{12Reference 12Agar OT et al. · 2015In vitroComparative studies on phenolic composition, antioxidant, wound healing and cytotoxic activities of selected Achillea L. species growing in Turkey — [in vitro]View study →}. A separate placebo-controlled cosmetic trial found a 2% extract improved epidermal differentiation markers and the appearance of skin surface over two months ^{6Reference 6Pain S et al. · 2011RCTSurface rejuvenating effect of Achillea millefolium extract — [randomised placebo-controlled]View study →}. Most positive wound-healing work in the genus, however, is on other Achillea species, and the human trial tested a topical ointment rather than the powdered herb of battlefield tradition.

Gap: Only one A. millefolium wound RCT, and it combined the herb with a standard base; the classic haemostatic (“stop bleeding”) claim itself has not been tested in a controlled human setting.

Yarrow is a consistent radical scavenger in vitro. Its essential oil strongly reduced the DPPH radical (IC₅₀ ≈ 1.6 µg/mL), scavenged hydroxyl radicals and inhibited lipid peroxidation ^{11Reference 11Candan F et al. · 2003In vitroAntioxidant and antimicrobial activity of the essential oil and methanol extracts of Achillea millefolium subsp. millefolium Afan. — [in vitro]View study →}. The activity tracks a phenolic fraction dominated by chlorogenic acid and flavonoids such as luteolin, apigenin, quercetin and rutin, all shown to scavenge free radicals and inhibit lipid peroxidation ^{12,14Reference 12Agar OT et al. · 2015In vitroComparative studies on phenolic composition, antioxidant, wound healing and cytotoxic activities of selected Achillea L. species growing in Turkey — [in vitro]View study →Reference 14Vitalini S et al. · 2011In vitroPhenolic compounds from Achillea millefolium L. and their bioactivity — [in vitro]View study →}. The sesquiterpene lactone achillolide A reduced reactive oxygen species and modulated MAPK signalling in cultured astrocytes and microglia, suggesting a cell-level protective role beyond simple scavenging ^{13Reference 13Elmann A et al. · 2016In vitroAchillolide A protects astrocytes against oxidative stress by reducing intracellular reactive oxygen species and interfering with cell signaling — [in vitro]View study →}. Essential oil from French-grown material confirmed the antioxidant profile ^{27Reference 27El-Kalamouni C et al. · 2017In vitroAntioxidant and antimicrobial activities of the essential oil of Achillea millefolium L. grown in France — [in vitro]View study →}. No human antioxidant-biomarker trial exists.

Gap: Entirely in vitro/cell-based; no evidence that oral yarrow raises antioxidant capacity or lowers oxidative markers in people.

The anti-inflammatory activity is mechanistically well-mapped but preclinical. Newly-described guaianolides from A. millefolium (millefolactons) inhibited 15-lipoxygenase and, for millefolacton C, suppressed nitric-oxide release, TNF-α, IL-6, PGE₂, iNOS, COX-2 and the NLRP3 inflammasome in LPS-stimulated microglial cells ^{15Reference 15Li H et al. · 2023In vitroGuaianolides from Achillea millefolium L. and their anti-inflammatory activity — [in vitro]View study →}. Yarrow extract and its flavonoid fraction inhibited human neutrophil elastase (IC₅₀ ≈ 20 µg/mL), a protease central to inflammation, giving a second distinct mechanism ^{16Reference 16Benedek B et al. · 2007In vitroAchillea millefolium L. s.l. — is the anti-inflammatory activity mediated by protease inhibition? — [in vitro]View study →}. The flavonoids and sesquiterpene lactones are the presumed active principles.

Gap: No human anti-inflammatory trial; the cytokine and enzyme effects come from isolated cells and rodent tissue at defined concentrations.

Yarrow shows genuine liver protection in animal models, consistent with its long use for hepatobiliary complaints. Pre-treatment with the crude extract (150–600 mg/kg) cut mortality and blunted the rise in ALT and AST in mice given hepatotoxic D-galactosamine plus lipopolysaccharide, with histology confirming preserved liver architecture ^{8Reference 8Yaeesh S et al. · 2006AnimalStudies on hepatoprotective, antispasmodic and calcium antagonist activities of the aqueous-methanol extract of Achillea millefolium — [mouse in vivo]View study →}. In streptozotocin-diabetic rats a hydroalcoholic extract lowered elevated liver enzymes alongside glucose and lipids, performing comparably to metformin on several markers ^{17Reference 17Rezaei S et al. · 2020AnimalHydroalcoholic extract of Achillea millefolium improved blood glucose, liver enzymes and lipid profile compared to metformin in streptozotocin-induced diabetic rats — [rat in vivo]View study →}. The effect plausibly reflects the combined antioxidant, anti-inflammatory and choleretic (bile-flow-stimulating) actions ^{23Reference 23Benedek B et al. · 2006AnimalCholeretic effects of yarrow (Achillea millefolium s.l.) in the isolated perfused rat liver — [rat in vivo]View study →} rather than a single mechanism.

Gap: No human hepatoprotective trial; doses are high relative to typical human intake, and the models are acute chemical injury rather than chronic liver disease.

Several rodent studies converge on a blood-pressure-lowering effect. The crude extract produced a dose-dependent fall in arterial pressure in anaesthetised rats, with negative inotropic/chronotropic effects on atria and verapamil-like relaxation of aortic rings ^{19Reference 19Khan AU · 2011AnimalBlood pressure lowering, cardiovascular inhibitory and bronchodilatory actions of Achillea millefolium — [rat in vivo]View study →}. A hydroethanolic extract and its dichloromethane fractions lowered mean arterial pressure in rats, and the isolated flavonoid artemetin reproduced the hypotension, partly via angiotensin-converting-enzyme inhibition ^{20Reference 20de Souza P et al. · 2011AnimalHypotensive mechanism of the extracts and artemetin isolated from Achillea millefolium L. in rats — [rat in vivo]View study →}. Two epimeric sesquiterpene lactones, leucodin and achillin, lowered pressure in spontaneously hypertensive rats through calcium-channel blockade and nitric-oxide-mediated vasorelaxation ^{21Reference 21Arias-Durán L et al. · 2021AnimalAntihypertensive and vasorelaxant effect of leucodin and achillin isolated from Achillea millefolium through calcium channel blockade and NO production: in vivo, functional ex vivo and in silico studies — [rat in vivo]View study →}. The signal is consistent and now traced to specific molecules, but remains entirely animal-level.

Gap: No human blood-pressure data; effective compounds are minor extract constituents whose oral bioavailability is unknown.

Yarrow has one positive human trial for menstrual pain. In a double-blind randomised study, female students with primary dysmenorrhea drank yarrow as a teabag preparation for three days across two cycles; the mean reduction in visual-analogue pain score was significantly greater than placebo at one and two months ^{2Reference 2Jenabi E · 2015RCTEffect of Achillea millefolium on relief of primary dysmenorrhea: a double-blind randomized clinical trial — [double-blind randomised]View study →}. The effect is biologically plausible given yarrow’s antispasmodic (calcium-channel) ^{9Reference 9Moradi MT et al. · 2013AnimalAntispasmodic effects of yarrow (Achillea millefolium L.) extract in the isolated ileum of rat — [rat in vivo]View study →} and anti-inflammatory (prostaglandin/COX-2) ^{15Reference 15Li H et al. · 2023In vitroGuaianolides from Achillea millefolium L. and their anti-inflammatory activity — [in vitro]View study →} activities, which target the uterine mechanisms of dysmenorrhoea. This is, however, a single small single-centre trial without objective endpoints.

Gap: One unreplicated trial; no measurement of prostaglandins or menstrual blood loss, and yarrow’s emmenagogue reputation was not addressed.

Antidiabetic activity is supported by rodent work only. A hydroalcoholic extract protected pancreatic β-cells in diabetic rats, an effect linked to down-regulation of IL-1β and iNOS gene expression — cytokines that drive β-cell destruction through the NF-κB inflammatory pathway ^{18Reference 18Zolghadri Y et al. · 2014AnimalAchillea millefolium L. hydro-alcoholic extract protects pancreatic cells by down regulating IL-1β and iNOS gene expression in diabetic rats — [rat in vivo]View study →}. In streptozotocin-diabetic rats the extract significantly lowered blood glucose, triglycerides and LDL-cholesterol while raising HDL, comparably to metformin on several endpoints ^{17Reference 17Rezaei S et al. · 2020AnimalHydroalcoholic extract of Achillea millefolium improved blood glucose, liver enzymes and lipid profile compared to metformin in streptozotocin-induced diabetic rats — [rat in vivo]View study →}. A registered human trial of a multi-herb “antidiabetic tea” containing yarrow exists, but its design cannot isolate yarrow’s contribution.

Gap: No controlled human data for yarrow alone; mechanism is inferred from gene-expression and glycaemic markers in chemically-induced diabetic rodents.

Central-nervous-system effects are early-stage but intriguing. A hydroalcoholic extract produced diazepam-like anxiolytic behaviour in the elevated-plus-maze and marble-burying tests in mice, reversed by the benzodiazepine antagonist flumazenil and confirmed by binding to the GABAₐ/benzodiazepine site — a defined GABAergic mechanism ^{24Reference 24Baretta IP et al. · 2012AnimalAnxiolytic-like effects of acute and chronic treatment with Achillea millefolium L. extract — [mouse in vivo]View study →}. In a triple-blind add-on RCT, one-year A. millefolium aqueous extract (250 or 500 mg/day) reduced the annualised relapse rate and lesion volume in multiple-sclerosis patients versus placebo ^{1Reference 1Ayoobi F et al. · 2019RCTAchillea millefolium is beneficial as an add-on therapy in patients with multiple sclerosis: a randomized placebo-controlled clinical trial — [randomised placebo-controlled]View study →}. An aqueous extract also reduced oxidative stress, apoptosis and memory impairment in the hippocampus of morphine-treated rats ^{25Reference 25Mozafari N et al. · 2022AnimalNeuroprotective effect of Achillea millefolium aqueous extract against oxidative stress and apoptosis induced by chronic morphine in rat hippocampal CA1 neurons — [rat in vivo]View study →}, echoing the astrocyte-protective action of achillolide A ^{13Reference 13Elmann A et al. · 2016In vitroAchillolide A protects astrocytes against oxidative stress by reducing intracellular reactive oxygen species and interfering with cell signaling — [in vitro]View study →}.

Gap: The MS trial is single and small with broad secondary endpoints; the rest is rodent behavioural/biochemical data with no anxiety or cognition trial in people.

One rigorous rodent study supports gastroprotection. In Wistar rats the aqueous extract protected gastric mucosa against ethanol- and indomethacin-induced acute lesions and healed acetic-acid-induced chronic ulcers (ED₅₀ ≈ 32 mg/kg), while a 28–90-day safety arm found only slight changes in liver weight, cholesterol and glucose ^{22Reference 22Cavalcanti AM et al. · 2006AnimalSafety and antiulcer efficacy studies of Achillea millefolium L. after chronic treatment in Wistar rats — [rat in vivo]View study →}. This aligns with the herb’s traditional use for dyspepsia and gastritis and complements its choleretic and anti-inflammatory actions.

Gap: Single species-specific animal study; no human gastric or dyspepsia trial with objective endpoints.

Antimicrobial activity is real in vitro but preparation-limited. The essential oil inhibited Streptococcus pneumoniae, Clostridium perfringens, Candida albicans, Mycobacterium smegmatis and other organisms, while the water-soluble extract was largely inactive ^{11Reference 11Candan F et al. · 2003In vitroAntioxidant and antimicrobial activity of the essential oil and methanol extracts of Achillea millefolium subsp. millefolium Afan. — [in vitro]View study →}; French-grown oil showed a similar profile ^{27Reference 27El-Kalamouni C et al. · 2017In vitroAntioxidant and antimicrobial activities of the essential oil of Achillea millefolium L. grown in France — [in vitro]View study →}. In a clinical trial, an aqueous-extract vaginal cream reduced vulvovaginal candidiasis symptoms but cleared Candida in fewer patients than clotrimazole, i.e. it was active but inferior to the standard antifungal ^{5Reference 5Zakeri S et al. · 2020RCTThe effect of Achillea millefolium L. on vulvovaginal candidiasis compared with clotrimazole: a randomized controlled trial — [randomised controlled trial]View study →}. Because the activity lives in the essential oil — whose composition and proazulene content vary widely between samples — a water infusion or tincture does not reliably deliver it.

Gap: Efficacy is tied to the volatile oil at concentrations tea/tincture may not reach; the one human antifungal trial showed inferiority to standard treatment.

Yarrow is generally well tolerated when used short-term at customary doses, and chronic dosing in rats produced only minor changes in liver weight and blood chemistry with no major organ toxicity ^{22Reference 22Cavalcanti AM et al. · 2006AnimalSafety and antiulcer efficacy studies of Achillea millefolium L. after chronic treatment in Wistar rats — [rat in vivo]View study →}. Its most established risk is allergic: as an Asteraceae (Compositae) plant rich in sesquiterpene lactones, yarrow can cause allergic contact dermatitis and cross-reacts within the Compositae group, so people sensitive to ragweed, chamomile, feverfew or chrysanthemums should use it cautiously ^{30Reference 30Cosmetic Ingredient Review (Andersen FA · 2001ReviewFinal report on the safety assessment of Yarrow (Achillea millefolium) Extract — [review]View study →}. Yarrow contains thujone and, in azulene-poor chemotypes, other monoterpenes whose content varies widely between samples, and only about half of commercial material meets European Pharmacopoeia quality standards ^{31Reference 31Benedek B et al. · 2008In vitroYarrow (Achillea millefolium L. s.l.): pharmaceutical quality of commercial samples — [in vitro]View study →}. Because rodent and in vitro studies show blood-pressure-lowering and smooth-muscle-relaxant activity, theoretical additive effects with antihypertensive and sedative medication are plausible though not formally studied in humans ^{20,24Reference 20de Souza P et al. · 2011AnimalHypotensive mechanism of the extracts and artemetin isolated from Achillea millefolium L. in rats — [rat in vivo]View study →Reference 24Baretta IP et al. · 2012AnimalAnxiolytic-like effects of acute and chronic treatment with Achillea millefolium L. extract — [mouse in vivo]View study →}; a high oral dose increased abnormal sperm in male rats, a finding of uncertain human relevance ^{29Reference 29Dalsenter PR et al. · 2004AnimalReproductive evaluation of aqueous crude extract of Achillea millefolium L. (Asteraceae) in Wistar rats — [rat in vivo]View study →}.

Scope of this safety review. No human drug-interaction study of yarrow exists — the antihypertensive and sedative additive-effect cautions above are theoretical, extrapolated from rodent hypotensive ^{20Reference 20de Souza P et al. · 2011AnimalHypotensive mechanism of the extracts and artemetin isolated from Achillea millefolium L. in rats — [rat in vivo]View study →} and GABAergic anxiolytic ^{24Reference 24Baretta IP et al. · 2012AnimalAnxiolytic-like effects of acute and chronic treatment with Achillea millefolium L. extract — [mouse in vivo]View study →} activity, and there are no CYP450 interaction data. Pregnancy and lactation have not been assessed in humans (see below). Absence of adverse reports is not evidence of safety.