Horny Goat Weed for Men: Dosage, Benefits and Side Effects

Icariin inhibits phosphodiesterase type 5, the enzyme that degrades cGMP in erectile tissue. Reported IC50 values for icariin against PDE5A1 sit in the micromolar range against sildenafil's nanomolar range, so the mechanism is shared and the potency is not. It shows some selectivity for PDE5 over PDE4.

• Erectile function: mechanistically plausible via PDE5 inhibition, but the evidence is laboratory and animal work rather than human randomised trials.
• Bone density: preliminary human work in postmenopausal women, using icariin-containing preparations.
• Fatigue and libido: traditional use, without controlled trial support.

This entry exists because the ingredient is common in the catalogue, not because the human evidence is strong. It is not.

Dell'Agli 2008 characterised PDE5 inhibition by icariin derivatives, and later structure-activity work explored analogues with much greater potency than the natural compound. What does not exist is a body of randomised human trials of epimedium supplements for erectile function, and the marketing generally does not distinguish between the two.

Supplements typically supply 250-1,000 mg/day of extract standardised to 10-20% icariin. There is no established human effective dose because the human dose-finding work has not been done. Products advertising very high icariin percentages are not therefore better studied.

Dizziness, dry mouth, nosebleeds and rapid heartbeat are reported. Because it shares a mechanism with PDE5 inhibitors it can lower blood pressure. Long-term safety data in humans is essentially absent.

Theoretically additive with prescription PDE5 inhibitors such as sildenafil and tadalafil, and with nitrates, where the combination can drop blood pressure dangerously. May interact with antihypertensives and anticoagulants. Anyone using an ED medication should not layer this on top without medical advice.