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Horny Goat Weed (Epimedium spp. / Icariin)
A traditional Chinese herb (icariin) marketed for libido and erectile function — but human ED evidence is weak; the better human evidence is actually for slowing bone loss in postmenopausal women.
What the evidence says
Most Horny Goat Weed studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2007–2026 with a typical study size of 100 participants.
Based on 25 studies · 1 meta-analysis · 2 RCTs · 158 total participants
Confidence
Moderate confidenceBy outcome
A 24-month RCT supports reduced bone loss in postmenopausal women, but the popular libido/erectile-function claims rest on weak human evidence graded poorly in supplement-ingredient reviews, with no meta-analyses.
No trials currently enrolling · 3 completed on ClinicalTrials.gov
2 of the completed trials have posted results
Registered trials show research momentum for Horny Goat Weed, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Horny goat weed (Epimedium species) is best known as a libido and erectile-dysfunction aid, on the rationale that its active icariin is a weak PDE5 inhibitor in the lab (the same enzyme sildenafil targets).
However, rigorous human ED trials are largely absent — reviews of popular ED supplements grade its evidence poorly.
The stronger human evidence is somewhere else entirely: Epimedium-derived flavonoids reduced bone loss in postmenopausal women in a 24-month randomized trial, fitting its phytoestrogenic, icariin-driven mechanism.
So it's best understood as an emerging bone-health phytoestrogen with popular-but-unproven male-vitality marketing.
Icariin inhibits PDE5 in vitro (the sildenafil target), the basis for erectile-function claims — but human confirmation is lacking.
Epimedium prenylflavonoids act as phytoestrogens that support osteoblast activity and bone density.
Icariin has antioxidant and anti-inflammatory activity in preclinical models.
How Horny Goat Weed works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Avoid — phytoestrogenic activity.
Avoid combining — theoretical additive vasodilation.
Avoid.
Icariin's weak PDE5 inhibition could theoretically add to blood-pressure-lowering effects — caution.
Possible additive bleeding risk; high doses have been linked to effects on clotting.
Phytoestrogenic activity may interact with estrogen-sensitive treatments. This interaction is awaiting review by a qualified pharmacist and has not been assigned a severity. It is shown so you can raise it, not because its risk has been established. Ask a pharmacist or prescriber before combining, and do not stop or change prescribed medicines based on this notice.
Tip: Lower dose; avoid combining with PDE5 drugs/nitrates
Tip: Take with food
Tip: Reduce dose
Horny Goat Weed has an evidence score of 4.2/10 — emerging evidence based on 25 indexed studies. A traditional Chinese herb (icariin) marketed for libido and erectile function — but human ED evidence is weak; the better human evidence is actually for slowing bone loss in postmenopausal women. Representative study: PMID 32358510.
Dosing for Horny Goat Weed: Standardized Epimedium extract providing icariin, about 250-740 mg of extract daily (icariin content varies widely). The highest cited extract dose is 740 mg a day of prenylflavonoid extract, for 6 weeks in postmenopausal women. The other dosed cited trial gave 60 mg icariin with 15 mg daidzein and 3 mg genistein a day. Label products go up to about 1,000 mg, above the highest dose in the cited trials. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Horny Goat Weed is with meals. Take it with food. Taken with food; product icariin content varies enormously, so standardize to icariin where possible.
Horny Goat Weed should be used with caution — talk to a healthcare provider before taking it. Reported side effects include dizziness/rapid heartbeat, hypomania/irritability (high doses), GI upset. How often they occur is not established for all of them. Use caution if any of these apply to you: Hormone-sensitive conditions (phytoestrogenic); Use of nitrates or PDE5 inhibitors (theoretical additive effect); Pregnancy and breastfeeding.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 25 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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