A new herbal product advertised as potency pill was sent for analysis by the local authority. The product was tested for the presence of potential derivatives of PDE-5 inhibitors, such as sildenafil, vardenafil, and tadalafil. Sildenafil analogues were identified, in which the piperazine ring and the sulfonyl group were replaced by a piperazinone and a hydroxyethyl structure, respectively. The chemical structures were established by LC–MS in ESI negative mode, UV and NMR spectroscopy (including DEPT, HSQC, HMBC, H,H-COSY, H,H-TOCSY and H,H-NOESY experiments). This is the first report of piperazinonafil and isopiperazinonafil as adulterant in an herbal food supplement.