Both sildenafil and RED BULL^®(energy drink) are claimed to boost up energy.RED BULL^®, one of the most commonly used energy drinks and its easily and widely available for daily use, the idea of this research work had arisen from observations about the concomitant use of sildenafil with RED BULL^® by men seeking for better sexual performance. To study the effect of RED BULL^® on the pharmacokinetic profile of sildenafil by using HPLC.The pharmacokinetic parameters (C_max, T_max and AUC) were determined in 10 rats following oral administration of 0.57 mg/ml sildenafil with and without RED BULL^® in crossover design, to achieve this purpose,simple, rapid and accurate method for validation and determination of sildenafil in rat plasma in the presence of RED BULL^® has been developed. This was performed using High-Performance Liquid Chromatography- Ultra Violet (HPLC-UV). The pharmacokinetic data showed that sildenafil plasma level was lower when combined with RED BULL^® According to the results obtained, maximum concentration (C_max) for sildenafil alone was (162.05 ng/ml) after 0.5 hours of administration. The C_max decreased to (44.68 ng/ml) after 0.5 hoursof administration RED BULL^® concomitantly with sildenafil which showed a significant effect on sildenafil plasma level (P<0.001). The area under the curve (AUC) decreased significantly from (370.53 ng/ml*hr) for sildenafil alone to (87.74 ng/ml*hr) when combined with RED BULL^®. RED BULL^® can alter sildenafil pharmacokinetic if they were taken together.