Interactions with Sexuality
6.1. Erections
Icariin is a selective PDE5 (enzyme) inhibitor with an IC50 value between 0.75-1.1mM depending on PDE5 isoform and an EC50 of about 4.62mmol/L in increasing cGMP in the corpus cavernosum of the penis; Icariin has approximately 100-fold greater affinity for PDE5 than other PDE isozymes. This effect can be potentiated by the modification of two hydroxyethyl ether moieties to the compound, which increase this inhibition 80-fold, but this modification is not naturally occurring. At 10mg/kg bodyweight in mice (110mg for a 150lb human) Icariin exerts pro-erectile properties and seems to have more effectiveness following repeated doses. It has shown efficacy over 30 days at 5-10mg/kg in an animal model of erectile dysfunction related to blood flow, which correlates to a 55-110mg dose for a 150lb man.
Other compounds in the Epimedium family that have PDE5 inhibitory potential are Icarisid II derived from Epimedium wanshanense (not significantly different in potency than Icariin; approximately half of Viagra)