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Botanical 5α-Reductase Inhibitors

This article was written by Eric Yarnell, ND, RH(AHG) and is protected by copyright, 2020.

With the exception of Serenoa repens (oral and topically) and Salvia rosmarinus​ (topically), none of these herbs has been shown to have this activity in humans. Extrapolation from in vitro or animal studies to humans is highly unlikely to lead to clinical efficacy.

* Serenoa repens (saw palmetto) fruit extract standardized to 70–95% fatty acids and sterols, 68% inhibition in one human clinical trial (PMID 9759701), 32% in another (PMID 11337315)

Note: As far as could be determined, this is the only human study in which the effect of an herb on 5α-reductase was determined. And no herb has been shown to decrease prostate size more than 1–2% (and only saw palmetto has really ever been shown to have even this tiny degree of shrinking effect), unlike the 30–50% reduction we see with drug 5α-reductase inhibitors. Thus it is likely 5α-reductase inhibition by herbs is working together with other properties of herbs to result in a net clinical effect that is manifestly different than drugs.

* Prunus africanum (pygeum, African plum) bark extract (which has a chemistry very similar to saw palmetto), in vitro ED50 0.78 mg/ml (PMID 23194959); inactive in another in vitro assay (PMID 8381228)

* Salvia rosmarinus = Rosmarinus officinalis (rosemary), in mice inhibited 5α-reductase 82% (200 µg/mL) and 95% (500 µg/mL) (PMID 22517595). This fits with a human clinical trial showing rosemary volatile oil topically improves hair growth (PMID 25842469).

* Phyllanthus niruri (stonebreaker), crude extract in vitro inhibited 5α-reductase by 24.3% (at 50 µg/mL) and 64.6% (at 200 µg/mL); its constituent stigmasterol glucoside IC40 = 27.2 µM; extract grew hair on mice at 5 mg po dose/day (PMID 30068884 )

* Ageratum conyzoides (billygoat weed, Brazilian chickweed), ex vivo suppressed mRNA expression of 5α-reductase type 1 and 2 genes (PMID 29048765)

* Lespedeza cuneata (Chinese bushclover), in rat model of BPH inhibited serum DHT by 51–54% (25–100 μg/ml) and expression of 5α-reductase by 54% (25 μg/ml), 61% (50 μg/ml), and 74% (100 μg/ml) (PMID 30724641 )

* Acorus gramineus (Japanese sweetflag), in mice 62–100% 5α-reductase inhibition (PMID 28830494)

* Curcuma longa (turmeric) crude extract IC50 = 9 μg/ml (27789379)

* Impatients balsamina (rose balsam) crude extract IC50 = 5.4 μg/ml (27789379)

* Carthamnus tinctorius (safflower) crude extract in vitro had a finasteride equivalent inhibition of 5α-reductase of 24 mg finasteride/1 g extract; it was the most potent of several herbal extracts at growing hair applied topically to mice (PMID 22178180 )

* Ganoderma lucidum (reishi) in vitro (PMID 23710567)

* Benincasa hispida (wax gourd) in vitro (PMID 23710567)

* Sphaeranthus indicus (East Indian globe thistle) in vitro (PMID 23710567)

* Cuscuta reflexa (giant dodder) in vitro (PMID 23710567)

* Torilis japonica (Japanese hedge parsley) a crude methanol extract was active in vitro, its compound torilin IC50 = 31.7 μM (PMID 12802730 ). Note that finasteride's IC50 was 0.38 μM in this assay.

* Brassica rapa (bok choy, napa cabbage) pollen, one compound (pollinastanol) had IC50 = 30 μM (PMID 19336936 )

* Cynomorium songaricum (suo yang) in mouse model of BPH, inhibited upregulation of 5α-reductase type 1 and 2 genes (PMID 30708032)

* Swertia bimaculata (double-spotted swertia), various xanthones inhibited 5α-reductase in vitro by 39–49% (PMID 28030961 )

* Avicennia marina (grey or white mangrove), in vitro crude extract (10 μg/ml) inhibited 5α-reductase 52%; avidequinone C inhibited 5α-reductase 1 with IC50 = 38.8 μM (PMID 24858268)


Notable Negatives

* Urtica dioica (stinging nettle) root in vitro (PMID 23194959; PMID 8381228)

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