Supplement analysis backed by scientific evidence · PT

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Horny Goat Weed

Horny goat weed (Epimedium) has no credible human trials for erectile dysfunction — the entire premise is in-vitro PDE5 inhibition by icariin that is orders of magnitude weaker than sildenafil. Its only decent randomized data are for bone loss, and this category is a hotspot for products spiked with prescription ED drugs.

What the science says

  • Improves erectile dysfunction Limited evidence

    Icariin does inhibit phosphodiesterase-5 in vitro, but at roughly 80-fold lower potency than sildenafil, and oral bioavailability is poor. There are no adequately designed, placebo-controlled human trials of Epimedium for erectile function using validated instruments such as the IIEF. Every claim here is extrapolated from cell and rodent work.

  • Prevents postmenopausal bone loss Limited evidence

    A 24-month randomized, double-blind, placebo-controlled trial in late postmenopausal women found Epimedium-derived flavonoids (60 mg icariin plus small amounts of daidzein and genistein daily) significantly slowed bone mineral density loss at the femoral neck and lumbar spine versus placebo. This is a single trial of a specific combination product with no fracture endpoints, and it has not been replicated — it does not make Epimedium a bone therapy.

  • Delivers meaningful icariin exposure from standard supplements Limited evidence

    A randomized, double-blind, placebo-controlled trial in postmenopausal women characterizing Epimedium prenylflavonoid pharmacokinetics and effects on bone-specific alkaline phosphatase and the osteoclast adaptor TRAF6 found the extract was tolerated but did not demonstrate the clear bone-turnover changes the mechanism predicts. Absorption of prenylflavonoids is variable and heavily dependent on preparation, so "10% icariin" on a label tells you little about what reaches the bloodstream.

  • Raises testosterone Limited evidence

    No human trial has shown Epimedium raises testosterone. The claim comes from the folk name and from animal studies at doses that do not translate.

Dosage & safety

Studied doseNo effective human dose is established for sexual function. The bone trial used a combination product supplying 60 mg icariin/day for 24 months. Commercial extracts standardized to 10-20% icariin are typically taken at 500-1,000 mg/day, which is a marketing convention rather than a studied dose.
SafetyReported effects include tachycardia, palpitations, dizziness, dry mouth, nosebleeds, and case reports of hypomania and of arrhythmia including AV block; severe hepatotoxicity has been described with Epimedium-containing products. The single largest hazard is adulteration — the FDA has repeatedly issued public notifications for "male enhancement" products, including horny goat weed formulas, found to contain undeclared sildenafil, tadalafil or unapproved analogues. That combination is potentially fatal with nitrates and dangerous with alpha-blockers or in cardiac disease. Epimedium also has phytoestrogenic activity, so avoid it with hormone-sensitive cancers, in pregnancy and while breastfeeding. It may add bleeding risk with anticoagulants. Buy only third-party-tested products, and treat any product that produces a dramatic same-day erectile effect as almost certainly adulterated.

Scientific references

Where to buy

NOW Foods, Horny Goat Weed Extract, 90 Tablets

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