Three voratin compounds (1-3) were isolated from the symbiotic marine dinoflagellate Effrenium voratum. The planar structures of 1-3 were determined by 1D and 2D NMR spectroscopy and HRESIMS, and the relative and absolute configurations were established using ROESY correlations, Mosher's method, and quantum calculations. All of the compounds are zwitterionic and contain a dihydroindolizinium ring and a spiroketal moiety. Compounds 1-3 were found to exhibit therapeutic effects against benign prostatic hyperplasia (BPH), as evaluated using testosterone propionate-treated LNCap and RWPE-1 human prostate cells. This excellent activity suggests that 1-3 are promising for the development of BPH treatments.