Vardenafil (VRE) is one of the most important drugs in the phosphodiesterase 5-inhibitors (PDE5) group. The usage of VRE must be carefully controlled if patients are taking certain medications that interact with it. Hence, to examine this critical need, a novel ternary nanocomposite consisting of conductive acetylene black (CAB) anchored with gold nanoparticles (GNP) (GNP@CAB) incorporated composite pencil graphite paste electrode (CPGPE) was prepared (GNP@CAB/CPGPE) and used for electrochemical detection of VRE drug. The nanostructural and morphological characteristics of GNP@CAB were examined using EDX, HRTEM and TEM techniques. The electrochemical properties of GNP@CAB/CPGPE were analyzed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). By employing the GNP@CAB/CPGPE electrode, the developed probe exhibited remarkable sensitivity and selectivity using adsorptive stripping square-wave voltammetry (AdS-SWV). The limits of detection and quantification for VRE were calculated to be 4.2 × 10⁻¹¹ M and 1.39 × 10⁻¹⁰ M, respectively. The practicality and reliability of the new electrode to determine the concentration of VRE in its commercial tablets and human biological fluids were achieved with good recoveries. To compare the electroanalytical method with an independent technique, the HPLC method was employed; nonsignificant differences were found between the two methods. Furthermore, for the first time, the interaction between VRE and the antihypertensive drug doxazosin on GNP@CAB/CPGPE was investigated using AdS-SWV. The large values of binding constants (K), ranging from 10⁶ to 10⁷, indicate a strong binding affinity between the two drugs. Additionally, thermodynamic parameters, including Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH), were evaluated. The results indicate that the interaction between VRE and doxazosin is predominantly hydrophobic, with the binding process being entropy-driven, thermodynamically favorable, and spontaneous.