Antiandrogenic

A double-blind randomised controlled trial of a 6% cream showed suppression of terminal hair growth over six months, with no adverse events reported ^{3Reference 3Vicente RA et al. · 2009RCTDouble-blind, randomised, placebo-controlled trial of a cream containing Stryphnodendron adstringens bark extract for suppressing terminal hair growth — randomised controlled trialView study →}. It is one of only two human trials this herb has.

The endpoint is topical and cosmetic. Nothing in the trial measures a systemic antiandrogenic effect, and the mechanism is unresolved.

The mechanistic work is the stronger half. Androgen-receptor-modulating galloyl monoterpene glycosides and pentagalloylglucose have been isolated from the root ^{12Reference 12Washida et al. · 2009In vitroAndrogen modulators from the roots of Paeonia lactiflora (paeoniae radix) grown and processed in Nara prefecture, Japan — in vitroView study →}, paeoniflorin downregulates CYP17A1 to curb testosterone over-secretion in primary murine theca cells ^{13Reference 13Ong et al. · 2019In vitroPaeoniflorin extract reverses dexamethasone-induced testosterone over-secretion through downregulation of cytochrome P450 17A1 expression in primary murine theca cells — in vitroView study →}, and a review places peony among the plant-derived anti-androgens ^{14Reference 14Grant et al. · 2012ReviewAn update on plant derived anti-androgens — reviewView study →}.

The single human datum is an early open, uncontrolled study of Shakuyaku-kanzo-to in 34 women with polycystic ovarian disease, reporting significantly reduced serum testosterone ^{10Reference 10Takahashi et al. · 1994Clinical trialEffect of TJ-68 (shakuyaku-kanzo-to) on polycystic ovarian disease — human clinical studyView study →}. In rats it was paeoniflorin plus glycyrrhizin that lowered ovarian androgen production ^{11Reference 11Takeuchi et al. · 1991AnimalEffect of paeoniflorin, glycyrrhizin and glycyrrhetic acid on ovarian androgen production — rat in vivoView study →}.

Shakuyaku-kanzo-to is the peony–licorice pairing, and licorice is independently active on this action, so a combination result cannot be assigned to peony.

The data point to reduced androgen synthesis rather than to aromatase induction, which peony is sometimes credited with.

The mechanistic claim rests on a single 1984 in-vitro study, in human foreskin fibroblasts rather than prostate tissue, in which a liposterolic extract inhibited both androgen metabolism and receptor binding ^{15Reference 15Sultan et al. · 1984In vitroInhibition of androgen metabolism and binding by a liposterolic extract of Serenoa repens in human foreskin fibroblasts — in vitroView study →}.

Downstream of that, a small placebo-controlled trial of a botanical 5α-reductase formulation reported improvement in about 60% of treated men with androgenetic alopecia against far fewer on placebo ^{16Reference 16Prager et al. · 2002RCTA randomized, double-blind, placebo-controlled trial of botanically derived inhibitors of 5α-reductase in androgenetic alopecia (RCT)View study →}. A two-year open-label study found 320 mg a day helped 38% of men against 68% on finasteride 1 mg ^{17Reference 17Rossi et al. · 2012RCTComparative effectiveness of finasteride vs Serenoa repens in male androgenetic alopecia: a two-year study — randomized comparative study (RCT)View study →}, and topical preparations were directionally similar ^{18Reference 18Wessagowit et al. · 2016Treatment of male androgenetic alopecia with topical products containing Serenoa repens extract — comparative studyView study →}.

Systemically the effect looks slight. PSA was unmoved in both large benign-prostatic-hyperplasia trials ^{19,20Reference 19Bent et al. · 2006RCTSaw palmetto for benign prostatic hyperplasia — randomized controlled trial (RCT)View study →Reference 20Barry et al. · 2011RCTEffect of increasing doses of saw palmetto extract on lower urinary tract symptoms — a randomized trial (RCT)View study →}, which is useful clinically — saw palmetto will not mask a rising PSA the way finasteride does.