Benefits
Bone density in late postmenopausal women (icariin-led flavonoid capsule)
In a 24-month placebo-controlled trial in 100 late postmenopausal women with low bone density, a daily capsule of 60 mg icariin plus 15 mg daidzein and 3 mg genistein kept spine and hip bone density steady while the placebo group lost bone. Both groups took calcium. Icariin was not tested alone, so the effect cannot be credited to it by itself.
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 a bone breakdown signal (TRAF6) only trended lower. This was an extract, not purified icariin, and it measured blood markers, not bone density or fractures.
PDE5 enzyme and erectile response in lab and rat studies
In enzyme tests icariin blocks PDE5, the enzyme that breaks down cGMP in penile smooth muscle, at micromolar concentrations, and oral icariin improved erectile pressure in rats with nerve injury. These are lab and animal results. One review found no published human studies of Epimedium for erectile function, and a later review called for high-quality clinical trials.
Testosterone and sperm measures 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, but 200 mg/kg increased oxidative stress in the testes. No human study measuring testosterone after icariin was found, so these animal results do not show an effect in men.
Mood and drinking measures in a 10-person open-label study
In 10 adults with bipolar disorder who were depressed and drinking heavily, icariin up to 300 mg/day for 8 weeks was followed by lower depression and anxiety scores and fewer heavy drinking days. There was no placebo group, so the change cannot be credited to icariin; the researchers advised controlled trials, not routine use.
Mechanism of action
Poor absorption and conversion by gut bacteria
Gut bacteria strip the glucose from icariin to form icariside II, and in lab tests one human gut strain went on to make icaritin and desmethylicaritin. In rats, 91.2% of an oral dose became icariside II. In human studies of Epimedium extracts, icariin itself was below detection in blood, so any effect likely depends on these metabolites.
PDE5 inhibition and cGMP in smooth muscle cells
In enzyme assays icariin inhibited PDE5 with IC50 values of roughly 0.75 to 5.9 micromolar, depending on the test, and raised cGMP in rat penile smooth muscle cells. Whether blood levels after oral intake ever reach these concentrations has not been shown in people.
Estrogen-like activity of the metabolites
Serum from rats given an Epimedium extract showed estrogen-like activity in human cell assays that tracked icaritin, desmethylicaritin and icariside I. In the 24-month human trial, however, the icariin capsule did not change blood estradiol or the thickness of the uterine lining.
Bone cells and bone mass in animal models
A meta-analysis of 7 studies in ovariectomized rats, a model of bone loss after menopause, found higher bone mineral density with icariin than with control, with wide variation between studies. The authors flagged study quality as a concern, and rat results do not establish an effect in women.
Clinical trials
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. Because the capsule held three flavonoids, the result cannot be assigned to icariin alone.
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, and the product was an extract, not purified icariin.
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); desmethylicaritin levels rose with dose. The study measured absorption only, not any health outcome.
Open-label, uncontrolled 8-week pilot of icariin with flexible dosing up to 300 mg/day; the registry entry (NCT01979133) describes a commercial horny goat weed supplement standardized to 20% icariin. (Xiao et al. 2016, Am J Drug Alcohol Abuse)
10 adults with bipolar I or II disorder, currently depressed, with active alcohol abuse or dependence, in Dallas, Texas.
Depression scores (HAMD, QIDS), anxiety scores (HAMA), heavy drinking days and standard drinks fell from baseline to week 8. Icariin was well tolerated and no one withdrew because of side effects. With no placebo group and only 10 people, the results cannot separate an icariin effect from natural change; the authors recommended controlled trials, not routine use.