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Willow Herb (Epilobium)

Epilobium parviflorum, Epilobium angustifolium
Evidence Level
Limited
2 Clinical Trials
6 Documented Benefits
2/5 Evidence Score

Willow herb is the dried flowering top of small-flowered willow herb (Epilobium parviflorum) and rosebay willow herb, also called fireweed (Epilobium angustifolium), plants of the evening primrose family. Despite the name, it is unrelated to willow bark. In Central Europe it became a popular tea for men's urinary comfort, and the European Medicines Agency accepts it as a traditional herbal medicine for lower urinary tract symptoms in men with a benign enlarged prostate, based on long-standing use rather than proven efficacy. Only one placebo-controlled trial has tested willow herb on its own: 128 men took a 500 mg extract or placebo for 6 months, and symptom scores and nighttime urination improved slightly more than on placebo, while prostate size did not change. The extract's maker sponsored that trial. New or changing urinary symptoms need a doctor's check first.

Studied Dose 500 mg/day of E. angustifolium extract standardized to at least 15% oenothein B (stated to equal 2 g of herb), one gastro-resistant capsule for 6 months. EU traditional tea: 1.5 to 2.0 g of cut herb in 250 ml boiling water, twice daily.
Active Compound Ellagitannins, chiefly the macrocyclic tannin oenothein B (the usual standardization marker; the trial extract contained at least 15%), with oenothein A, flavonoids (quercetin, myricetin and kaempferol glycosides) and phenolic acids.

Benefits

Urinary symptom scores in older men

In a 6-month placebo-controlled trial in 128 men in their mid 60s with a benign enlarged prostate, a 500 mg daily extract lowered the International Prostate Symptom Score from 13.4 to 11.5 points, while placebo went from 13.0 to 13.6. The gap of about 2.5 points is small, and it comes from a single trial sponsored by the extract's maker.

Supported by Trial 1

Nighttime urination in men

In the same trial, trips to urinate on the night before each visit fell from an average of 1.2 to 0.8 with the extract and rose from 1.1 to 1.3 with placebo, a difference the authors' statistical model found significant. The men started with mild nighttime urination, and the count came from a single night before each visit.

Supported by Trial 1, Trial 2

Urine left in the bladder after voiding

Residual urine after voiding, measured by ultrasound, was a main outcome. The authors reported a significant shift toward lower volumes with the extract, but the group average barely moved (40.4 to 39.5 ml, against 28.0 to 31.4 ml on placebo), and the extract group started higher. Prostate size, the other main outcome, did not differ from placebo.

Supported by Trial 1

Traditional EU herbal tea for men's urinary comfort

The European Medicines Agency recognizes willow herb tea as a traditional herbal medicine for relief of lower urinary tract symptoms linked to a benign enlarged prostate, to be used only after a doctor has excluded serious conditions. This rests on use in Austria, Germany and Poland since at least the early 1980s; its review found no clinical efficacy studies.

Supported by Trial 1, Trial 2

Multi-herb formulas that include willow herb

In a 3-month placebo-controlled trial in 57 men with a benign enlarged prostate, a daily capsule of small-flowered willow herb with saw palmetto, pygeum, pumpkin seed and lycopene cut median symptom scores by 36% against 8% and lowered day and night urination. Small uncontrolled studies of other blends reported gains. None can show what willow herb adds.

Supported by Trial 2, Trial 1

Oenothein B and prostate cell activity in lab studies

In enzyme tests, oenothein B from willow herb blocked 5-alpha-reductase, which converts testosterone to DHT, and partly blocked aromatase. Willow herb extracts and urolithins, which gut bacteria make from its tannins, slowed prostate cell growth and PSA release in cell culture, and an extract eased testosterone-induced prostate enlargement in rats. These are lab and animal findings.

Supported by Trial 1

Mechanism of action

1

Oenothein B inhibits enzymes that make DHT (enzyme assays)

Activity-guided studies of small-flowered and other willow herbs identified the ellagitannins oenothein B and oenothein A as the compounds that inhibit 5-alpha-reductase and aromatase in test-tube assays. The European Medicines Agency found no human data showing these effects after oral use.

2

Gut bacteria turn its tannins into urolithins

The extract's polyphenols degraded in a lab model of stomach and small intestine digestion, and in mice urolithins, the gut-bacteria products of these tannins, appeared only after repeated dosing. Human gut bacteria converted tannins from a related willow herb species into urolithins, which slowed prostate cell growth in culture. Lab and animal findings.

3

Anti-inflammatory and enzyme effects in prostate cells and rats

A willow herb water extract and oenothein B raised activity of neutral endopeptidase, a peptide-degrading enzyme, in prostate cancer cells. In testosterone-treated rats, an oral extract lowered androgen levels, NF-kB expression, inflammation and oxidative stress in the prostate. These are cell and animal results.

Clinical trials

1
Willow Herb Extract 500 mg/day: 6-Month Placebo-Controlled Trial in 128 Men (maker-sponsored)
PubMed

Single-center, randomized, double-blind, placebo-controlled trial in Benevento, Italy, of one gastro-resistant capsule a day of E. angustifolium extract (ENOTprost, at least 15% oenothein B) for 6 months; registered as ISRCTN18705154 with the extract maker EPO Srl as sponsor and funder. (Esposito et al. 2021, Biomed Pharmacother)

128 men with a benign enlarged prostate diagnosed by ultrasound, blood tests and symptom score, not taking prostate drugs (70 extract, 58 placebo; mean age 67 and 64). Baseline symptom scores were moderate (about 13 points) and nighttime urination mild (about 1 trip).

Prostate volume, a main outcome, did not change differently between groups. For residual urine, the other main outcome, the authors' model showed a significant shift toward lower volumes, although means barely changed (40.4 to 39.5 ml vs 28.0 to 31.4 ml). Symptom scores went from 13.4 to 11.5 vs 13.0 to 13.6 on placebo, and nighttime trips from 1.2 to 0.8 vs 1.1 to 1.3. PSA showed no treatment effect, and the blood neutrophil to lymphocyte ratio, an inflammation marker and a secondary outcome, did not change over time. No extract-related adverse effects were reported and liver and kidney tests showed no treatment effect. Two authors were employees of the maker, and the registry entry listed at least 5 months of treatment and different, narrower entry criteria than the paper reports.

2
Herbal Blend with Small-Flowered Willow Herb (ProstateEZE Max): 3-Month Placebo-Controlled Trial
PubMed

Phase II randomized, double-blind, placebo-controlled trial of one capsule a day of a blend of pumpkin seed (Cucurbita pepo), Epilobium parviflorum, lycopene, pygeum and saw palmetto for 3 months. (Coulson et al. 2013, Complement Ther Med)

57 otherwise healthy men aged 40 to 80 with medically diagnosed benign prostatic hyperplasia (32 blend, 25 placebo).

Median symptom score (IPSS) fell 36% on the blend against 8% on placebo (p < 0.05). Daytime urination fell from 7.0 to 5.9 times a day (placebo 6.2 to 6.3) and nighttime urination from 2.9 to 1.8 (placebo 2.8 to 2.6). The blend was reported as well tolerated. With five ingredients, the effect of willow herb alone cannot be separated, and the abstract does not name the funder.

Side effects and drug interactions

Common Potential side effects

In the 6-month trial of 500 mg/day, no man reported side effects related to the extract, and liver and kidney blood tests showed no treatment effect.
The EU herbal monograph lists no known side effects; its 2022 review found a single EU safety report linked to willow herb (vertigo after a homeopathic product, in a patient taking many other medicines).
Do not use if you are allergic to willow herb. Tests for reproductive toxicity, genotoxicity and carcinogenicity have not been done, and the monograph gives no use for people under 18.
Urinary symptoms can have serious causes. See a doctor before use, and promptly if symptoms worsen or you develop fever, spasms, blood in the urine, painful urination or trouble passing urine.

Important Drug interactions

The EU herbal monograph reports no known drug interactions, and its assessment found no human interaction data.
In rat studies, willow herb extracts changed the expression of enzymes that process drugs and steroid hormones; regulators judged any effect in people hypothetical. Ask a pharmacist if you take prescription medicines.
Alpha-blockers and 5-alpha-reductase inhibitors (such as tamsulosin or finasteride): men taking them were excluded from the single-herb trial, so combined use is untested there. Do not replace a prescribed medicine without your doctor.
Multi-herb prostate formulas often pair willow herb with saw palmetto, pygeum or nettle root; check the label for every ingredient.

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Frequently asked questions about Willow Herb (Epilobium)

Is willow herb related to willow bark?

No. Willow herb is the leafy flowering top of Epilobium plants from the evening primrose family (Onagraceae). Willow bark comes from willow trees (Salix) and supplies salicin, which the body turns into salicylic acid, the same active metabolite aspirin produces. They are sold for different purposes; see our white willow bark page.

Which willow herb species is used: small-flowered or fireweed?

The EU monograph covers both small-flowered willow herb (E. parviflorum) and rosebay willow herb or fireweed (E. angustifolium). The herbalist whose books made the tea popular recommended only small-flowered species, but both have been sold since the 1980s. The only single-herb trial used a fireweed extract standardized to oenothein B.

How strong is the evidence for willow herb and men's urinary comfort?

Limited. One 6-month trial in 128 men, sponsored by the extract's maker, found small gains in symptom score and nighttime urination over placebo and no change in prostate size. EU regulators reviewed that trial in 2022 and kept the herb's traditional-use status, noting the extract was not adequately described. Other studies tested multi-herb blends.

Will willow herb affect a PSA blood test?

In the 6-month trial, PSA showed no treatment effect compared with placebo. In cell culture, willow herb compounds lowered PSA release from prostate cells, but that has not been seen in men. This is one study, so tell your doctor you take it before any PSA test.

When should urinary symptoms be checked by a doctor first?

Always before starting. The EU monograph says willow herb should be used only after a doctor has excluded serious conditions, and that you should see a doctor if symptoms worsen or if fever, spasms, blood in the urine, painful urination or trouble passing urine appear. These warning signs can point to problems that need medical treatment.

What is Willow Herb?

Willow herb is the dried flowering top of small-flowered willow herb (Epilobium parviflorum) and rosebay willow herb, also called fireweed (Epilobium angustifolium), plants of the evening primrose family. Despite the name, it is unrelated to willow bark.

What is Willow Herb used for?

Willow Herb is researched primarily for Kidney/Urinary Tract and Prostate Health. In a 6-month placebo-controlled trial in 128 men in their mid 60s with a benign enlarged prostate, a 500 mg daily extract lowered the International Prostate Symptom Score from 13.4 to 11.5 points, while placebo went from 13.0 to 13.6.

What is the recommended dosage of Willow Herb?

The clinically studied dose is 500 mg/day of E. angustifolium extract standardized to at least 15% oenothein B (stated to equal 2 g of herb), one gastro-resistant capsule for 6 months. EU traditional tea: 1.5 to 2.0 g of cut herb in 250 ml boiling water, twice daily. Always follow the product label and check with a healthcare provider for personal advice.

Is Willow Herb safe, and does it have side effects?

Side effects and cautions reported for Willow Herb include: In the 6-month trial of 500 mg/day, no man reported side effects related to the extract, and liver and kidney blood tests showed no treatment effect. It may also interact with some medications. Willow Herb is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Willow Herb interact with any medications?

Possible interactions include: The EU herbal monograph reports no known drug interactions, and its assessment found no human interaction data. In rat studies, willow herb extracts changed the expression of enzymes that process drugs and steroid hormones; regulators judged any effect in people hypothetical. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Willow Herb?

NutraSmarts rates the evidence for Willow Herb as Limited (2 out of 5). It is backed by 2 study summaries and 14 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(14 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Esposito C, Santarcangelo C, Masselli R, Buonomo G, Nicotra G, Insolia V, D'Avino M, Caruso G, Buonomo AR, Sacchi R, Sommella E, Campiglia P, Tenore GC, Daglia M. Epilobium angustifolium L. extract with high content in oenothein B on benign prostatic hyperplasia: A monocentric, randomized, double-blind, placebo-controlled clinical trial. Biomed Pharmacother. 2021;138:111414. doi: 10.1016/j.biopha.2021.111414.PubMedUsed to support: Randomized, double-blind, placebo-controlled single-center trial in 128 Italian men with benign prostatic hyperplasia: 500 mg/day of an E. angustifolium extract (at least 15% oenothein B) for 6 months. Prostate volume did not change differently from placebo; the authors' model showed a shift toward lower residual urine although group means barely moved (40.4 to 39.5 ml vs 28.0 to 31.4 ml). Symptom score went from 13.4 to 11.5 vs 13.0 to 13.6, and nighttime urination from 1.2 to 0.8 vs 1.1 to 1.3. PSA showed no treatment effect, no adverse effects were reported, and liver and kidney tests showed no treatment effect. Two authors were employees of the extract maker EPO Srl, which partly funded the work through a research contract.
  2. Coulson S, Rao A, Beck SL, Steels E, Gramotnev H, Vitetta L. A phase II randomised double-blind placebo-controlled clinical trial investigating the efficacy and safety of ProstateEZE Max: a herbal medicine preparation for the management of symptoms of benign prostatic hypertrophy. Complement Ther Med. 2013;21(3):172-9. doi: 10.1016/j.ctim.2013.01.007.PubMedUsed to support: Phase II randomized, double-blind, placebo-controlled trial in 57 men with medically diagnosed benign prostatic hyperplasia: a once-daily capsule combining pumpkin seed, Epilobium parviflorum, lycopene, pygeum and saw palmetto for 3 months reduced median IPSS by 36% vs 8% on placebo and lowered day and night urination frequency. A combination, so the contribution of willow herb cannot be isolated.
  3. Orlando G, Chiavaroli A, Ferrante C, Recinella L, Leone S, Brunetti L, Di Simone SC, Menghini L, Petrucci M, Zengin G, Cesaroni F, Pontarelli G, Cindolo L, Neri F. Protective effects induced by the food supplement Fluxonorm® in the lower urinary tract. Eur Rev Med Pharmacol Sci. 2021;25(7):3074-3082. doi: 10.26355/eurrev_202104_25562.PubMedUsed to support: Uncontrolled study in 30 patients with lower urinary tract symptoms and benign prostatic hyperplasia on standard care: adding a 1,200 mg/day tablet of five plant extracts including E. angustifolium for 30 days was reported to improve all clinical parameters, including maximum flow; no figures in the abstract. Also cell experiments on prostate cancer cells and PGE2 production.
  4. Chiavaroli A, Acquaviva A, Simone SCD, Salvatore S, Messina S, Morgante C, Lupi C, Villa S, Zengin G, Orlando G, Menghini L, Ferrante C, Schips L, Cindolo L, Marchioni M. Protective Effects Induced by a Novel Food Supplement Based on Epilobium angustifolium, Ptychopetalum olacoides, Ginkgo biloba, and Equisetum arvense Extracts and Citrulline in the Lower Urinary Tract: Preclinical and Clinical Evidence. Phytother Res. 2026;Online ahead of print (2026 Sep 1). doi: 10.1002/ptr.70438.PubMedUsed to support: Retrospective, non-randomized multicenter review of 59 men with urinary symptoms from benign prostatic hyperplasia and mild erectile dysfunction given a supplement of E. angustifolium, muira puama, ginkgo, horsetail and citrulline, alone or with prescription drugs; the authors report improved urine flow and symptom outcomes. Also anti-inflammatory gene-expression effects in isolated mouse prostate tissue.
  5. Dacrema M, Sommella E, Santarcangelo C, Bruno B, Marano MG, Insolia V, Saviano A, Campiglia P, Stornaiuolo M, Daglia M. Metabolic profiling, in vitro bioaccessibility and in vivo bioavailability of a commercial bioactive Epilobium angustifolium L. extract. Biomed Pharmacother. 2020;131:110670. doi: 10.1016/j.biopha.2020.110670.PubMedUsed to support: Lab and mouse study of a commercial E. angustifolium extract standardized to at least 15% oenothein B: its polyphenols degraded during simulated stomach and duodenal digestion, and in mice urolithins appeared only after prolonged treatment. Three authors were from the extract maker EPO Srl.
  6. Lesuisse D, Berjonneau J, Ciot C, Devaux P, Doucet B, Gourvest JF, Khemis B, Lang C, Legrand R, Lowinski M, Maquin P, Parent A, Schoot B, Teutsch G. Determination of oenothein B as the active 5-alpha-reductase-inhibiting principle of the folk medicine Epilobium parviflorum. J Nat Prod. 1996;59(5):490-2. doi: 10.1021/np960231c.PubMedUsed to support: Enzyme study from a pharmaceutical company lab: an aqueous extract of Epilobium parviflorum inhibited 5-alpha-reductase, and the active compound was isolated and identified as the macrocyclic tannin oenothein B. Test-tube evidence only.
  7. Ducrey B, Marston A, Göhring S, Hartmann RW, Hostettmann K. Inhibition of 5 alpha-reductase and aromatase by the ellagitannins oenothein A and oenothein B from Epilobium species. Planta Med. 1997;63(2):111-4. doi: 10.1055/s-2006-957624.PubMedUsed to support: Activity-guided fractionation of Epilobium species identified oenothein A and oenothein B as the main constituents inhibiting 5-alpha-reductase and aromatase in enzyme assays; oenothein B made up as much as 14% of crude plant extracts across 10 species. Test-tube evidence only.
  8. Stolarczyk M, Piwowarski JP, Granica S, Stefańska J, Naruszewicz M, Kiss AK. Extracts from Epilobium sp. herbs, their components and gut microbiota metabolites of Epilobium ellagitannins, urolithins, inhibit hormone-dependent prostate cancer cells-(LNCaP) proliferation and PSA secretion. Phytother Res. 2013;27(12):1842-8. doi: 10.1002/ptr.4941.PubMedUsed to support: Cell-culture study: extracts of E. angustifolium, E. parviflorum and E. hirsutum inhibited the growth and PSA secretion of hormone-dependent prostate cancer cells (LNCaP), with oenothein B the strongest constituent. Ellagitannins from E. hirsutum were converted by human gut microbiota into urolithins, which were also active in these cells. Lab evidence only.
  9. Deng L, Zong W, Tao X, Liu S, Feng Z, Lin Y, Liao Z, Chen M. Evaluation of the therapeutic effect against benign prostatic hyperplasia and the active constituents from Epilobium angustifolium L. J Ethnopharmacol. 2019;232:1-10. doi: 10.1016/j.jep.2018.11.045.PubMedUsed to support: Cell and rat study: E. angustifolium extracts reduced viability of prostate (BPH-1) cells and PSA secretion in LNCaP cells, and an oral n-butanol extract (100 to 400 mg/kg for 28 days) showed effects against testosterone-induced prostate enlargement in rats, with lower androgen levels, reduced NF-kB expression, inflammation and oxidative stress. Animal and lab evidence only.
  10. Kiss A, Kowalski J, Melzig MF. Induction of neutral endopeptidase activity in PC-3 cells by an aqueous extract of Epilobium angustifolium L. and oenothein B. Phytomedicine. 2006;13(4):284-9. doi: 10.1016/j.phymed.2004.08.002.PubMedUsed to support: Cell study: an aqueous E. angustifolium extract and oenothein B induced neutral endopeptidase activity in PC-3 prostate cancer cells, did not affect ACE, and weakly inhibited cell proliferation. Lab evidence only.
  11. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). European Union herbal monograph on Epilobium angustifolium L. and/or Epilobium parviflorum Schreb., herba (EMA/HMPC/712511/2014). European Medicines Agency. 2015;Final, adopted 24 November 2015..SourceUsed to support: Not PubMed-indexed. Traditional-use (not well-established-use) monograph: willow herb tea for relief of lower urinary tract symptoms related to benign prostatic hyperplasia after serious conditions have been excluded by a doctor; 1.5 to 2.0 g in 250 ml boiling water twice daily; long-term use possible; contraindicated in hypersensitivity; see a doctor for fever, spasms, blood in the urine, painful urination or urinary retention; no known side effects or interactions; no relevant use under 18; reproductive toxicity, genotoxicity and carcinogenicity tests not performed.
  12. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Assessment report on Epilobium angustifolium L. and/or Epilobium parviflorum Schreb., herba (EMA/HMPC/712510/2014). European Medicines Agency. 2015;Final, adopted 24 November 2015..SourceUsed to support: Not PubMed-indexed. Documents use of willow herb tea in Austria, Germany and Poland since at least 1982 for prostate complaints (popularized by the books of herbalist Maria Treben, who recommended small-flowered species), accepts traditional use only for the prostate indication, finds no clinical pharmacology, efficacy or safety studies, summarizes enzyme and cell data on oenotheins, and notes rat studies on drug-metabolizing enzyme expression whose consequences in people are hypothetical.
  13. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Addendum to Assessment report on Epilobium angustifolium L. and/or Epilobium parviflorum Schreb., herba (EMA/HMPC/615965/2022). European Medicines Agency. 2022;Adopted 21 September 2022..SourceUsed to support: Not PubMed-indexed. Periodic review that assessed the 128-man extract trial: the herbal preparation was not adequately described, the study used a non-medicinal product, and no E. angustifolium extract had been in EU medicinal use for more than 10 years, so no revision to well-established use; the absence of adverse events was noted, and EudraVigilance held one Epilobium-related report (vertigo after a homeopathic product taken with many other medicines). No revision of the monograph.
  14. ISRCTN Registry (sponsor and funder: EPO Srl). The effect of Epilobium angustifolium L. supplement on prostate health (ISRCTN18705154). ISRCTN Registry. 2020;Registered 19 June 2020; last edited 13 August 2021. doi: 10.1186/ISRCTN18705154.SourceUsed to support: Not PubMed-indexed. Registry record for the 128-man trial: sponsor and funder EPO Srl; primary outcomes post-void residual and prostate volume; registered treatment of at least 5 months, with entry criteria of IPSS 8 to 19, prostate volume 25 to 70 cc and residual urine 30 to 200 ml, narrower than those in the published paper. The registry also lists pharmacologically treated but uncontrolled BPH as an entry criterion, while the paper excluded men on prostate drugs, and it gives enrolment from 22 to 30 June 2020 with completion on 15 December 2020, under 6 months after the last enrolment.