Benefits
PDE5 enzyme inhibition in laboratory tests
In enzyme tests icariin, the main Epimedium flavonoid, blocked PDE5, the enzyme that breaks down cGMP in penile smooth muscle, at concentrations of about 0.75 to 5.9 micromolar, depending on the test, and it raised cGMP in rat smooth muscle cells. In people, icariin itself was below detection in blood after Epimedium extracts were swallowed, so whether this happens after oral use is unknown.
Bone density in late postmenopausal women (Epimedium flavonoid capsule)
In a 24-month placebo-controlled trial in 100 late postmenopausal women with low bone density, a daily capsule of Epimedium-derived flavonoids (60 mg icariin, 15 mg daidzein, 3 mg genistein) kept spine and hip bone density steady while the placebo group lost bone; both groups took calcium. This was a defined flavonoid mix, not a typical herb extract, and fractures were not studied.
Sexual behavior in animal studies (no human trial)
Epimedium has a long history of use in Traditional Chinese Medicine for sexual function, but no placebo-controlled human trial of it for libido, erections or sexual satisfaction was found. A review of herbal products for erectile function listed Epimedium among herbs studied only in laboratory and animal models, and a later review called for high quality clinical trials with large samples.
Bone formation marker with an Epimedium prenylflavonoid extract
In 58 healthy postmenopausal women, 740 mg a day of an Epimedium prenylflavonoid extract for 6 weeks was followed by higher levels of the bone formation marker BSAP, while an osteoclast signal (TRAF6) only trended lower. These are blood markers, not bone density or fractures.
Mechanism of action
PDE5 Inhibition
In enzyme assays icariin inhibited PDE5 with IC50 values of 0.75 to 1.1 micromolar in one study and 5.9 micromolar in another, and kept cGMP higher in rat penile smooth muscle cells. More cGMP relaxes smooth muscle, the proposed route to an erectile effect. This chain has been shown in laboratory and animal work only, and blood levels of icariin after oral intake were below detection in human studies.
Estrogen-Like Signaling
A review reports that Epimedium prenylflavonoids act on estrogen signaling in bone cell lines. In the 24-month human trial, however, the Epimedium flavonoid capsule did not change blood estradiol or the thickness of the uterine lining.
Testosterone in Male Rat Studies
In adult male rats, oral icariin at 50 and 100 mg/kg for 35 days raised testosterone, and 100 mg/kg raised sperm counts, while 200 mg/kg increased oxidative stress in the testes. No human study measuring testosterone after epimedium or icariin was found, so these results do not show an effect in men.
Bone Cell Signaling in Lab and Animal Studies
A review reports that about nine Epimedium prenylflavonoids act on estrogen signaling and other bone-building pathways in stem cells, osteoblasts and osteoclasts, and that enriched extracts benefited bone in estrogen-deficient animal models. These are lab and animal findings.
Absorption and Metabolites in People
In two human studies of a standardized Epimedium prenylflavonoid extract, icariin itself stayed below detection in blood. The compounds that appeared were metabolites: icariside II, peaking about 4 hours after a dose, and desmethylicaritin, peaking about 24 hours after, which rose with dose; icaritin was also detected in one study.
Clinical trials
Randomized, placebo-controlled single-dose study of a standardized Epimedium prenylflavonoid extract at 370, 740 or 1110 mg, with blood sampled over 48 hours. (Teo et al. 2019, Planta Med)
30 healthy men.
The extract was well tolerated with no adverse effects observed. Icariin, icariside I and icaritin stayed below detection limits; the circulating compounds were icariside II (peak about 4 hours) and desmethylicaritin (peak about 24 hours), and desmethylicaritin levels rose with dose. The study measured absorption only, not any health outcome.
Randomized, double-blind, placebo-controlled 24-month trial of Epimedium-derived phytoestrogen flavonoids (60 mg icariin, 15 mg daidzein and 3 mg genistein daily); both groups took 300 mg calcium daily. (Zhang et al. 2007, J Bone Miner Res)
100 healthy late postmenopausal women, 10 to 18 years past menopause, with lumbar spine T-scores between -2 and -2.5; 85 completed.
Bone density was maintained on the capsule (spine +1.3% and femoral neck +1.6% at 24 months, not significant within the group) and fell on placebo (spine -2.4%, femoral neck -1.8%). The between-group differences were significant at 24 months (spine p = 0.006, femoral neck p = 0.008). The resorption marker deoxypyridinoline fell 39 to 43%; osteocalcin did not change. Estradiol and endometrial thickness were unchanged. The capsule was a defined three-flavonoid mix, so the result does not describe every epimedium product.
Randomized, double-blind, placebo-controlled trial of a purified Epimedium prenylflavonoid extract (740 mg daily for 6 weeks); main outcomes were safety and pharmacokinetics. (Yong et al. 2021, Phytomedicine)
58 healthy postmenopausal women in Singapore, mean age 57.9 years.
No significant adverse symptoms and no changes in liver, blood or kidney tests. Icariin and icariside I were below detection in serum; desmethylicaritin was the main metabolite. The bone formation marker BSAP was higher (p < 0.05) and the osteoclast protein TRAF6 showed only a trend (p = 0.068). Blood markers only; bone density was not measured.