What natural herb or medicine is good for ed?

OTC ED supplements: While there is no specific "natural"/otc preparation to "treat" ed, l-arginine is a precursor for the synthesis of Nitric Oxide - the vasodilator which initiates erections. This has been "recommended" (not "prescribed"); often in conjunction with proanthocyanidins or yohimbime.

Complicated Q&A: Semantics play a major role in answering your question. No "natural" "organic" herbs or supplements have peer-reviewed published randomized controlled trial data supporting their use in treating ed. Many otc & prescription medications are derived originally from natural sources but are now manufactured eg yohimbine from yohimbe. All fda-approved medications have published data as being good for ed.