The Willow herb is considered a common weed but may have potential benefit in prostate disorders. Oenothein B, a substance in willow herb, appears to have 5-alpha-reductase inhibitory activity.

Willow Herb Research Update
Studies on antibacterial, anti-inflammatory and antioxidant activity of herbal remedies used in the treatment of benign prostatic hyperplasia and prostatitis.
J Ethnopharmacol. 2006 Jan 3;103(1):71-5. Epub 2005 Aug 24. Department of Urology, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa.
Crude water and ethanolic extracts of five herbal remedies reported in the literature for traditional treatment of benign prostatic hyperplasia (BPH) and/or prostatitis were investigated for their effect on hydroxyl scavenging activity, antibacterial activity and their ability to inhibit cyclooxygenase-1 and -2 (COX-1 and COX-2) catalysed prostaglandin biosynthesis. Both the water and ethanol extracts of Hypoxis hemerocallidea and Epilobium parviflorum inhibited the growth of Escherichia coli. All 10 extracts scavenged the hydroxyl radical but with various potencies (32-93%). Ethanolic extracts were the most active in inhibiting COX-1 catalysed prostaglandin biosynthesis. The ethanolic extract of Epilobium parviflorum showed inhibitory effects on both the COX-1 and -2 catalysed prostaglandin biosynthesis, inhibited growth of Escherichia coli and exerted antioxidant activity. Although these results support the traditional use of Epilobium parviflorum for treatment of prostatitis and BPH, further investigation is required, for this promising plant.

Determination of oenothein B as the active 5-alpha-reductase-inhibiting principle of the folk medicine Epilobium parviflorum.
J Nat Prod. 1996 May;59(5):490-2. Centre de Recherche ROUSSEL UCLAF, Roumainville, France.
Several extracts from Epilobium parviflorum, the willow herb plant used in Central Europe for the treatment of prostate disorders, were evaluated in a biochemical assay with 5-alpha-reductase. The aqueous willow herb extract displaying inhibition of the enzyme was analyzed, the fraction responsible for this activity was purified, and the active compound identified as a macrocyclic tannin, oenothein B.

Willow Herb questions
Q. Can willow herb be used the same time as ahcc supplement?
   A. We have not seen any studies with this combination, so it is difficult to say for sure. Many herbs and supplements can be combined safely if the dosage used of each is low.