Icariin is a flavonoid pulled from *Epimedium* plants, also called horny goat weed. Lab and animal work shows it blocks PDE5 enzymes and nudges nitric oxide pathways. Human data for icariin by itself remains thin.
Traditional medicine systems have long used *Epimedium* extracts for vitality and sexual health. Your body struggles to absorb icariin well on its own. Its breakdown product icaritin probably does more of the heavy lifting inside you.
Most supplements sell icariin as a standardized *Epimedium* extract, not the pure compound. Dose suggestions vary wildly from product to product because solid human trials never pinned down a standard amount.
Watch for blood pressure trouble if you mix icariin with nitrate drugs like nitroglycerin or ED pills like sildenafil. That combo can send your pressure crashing.