In recent decades, the so-called "new pollutants" have received increasing attention in the field of research and environmental protection. The term "new pollutants" includes all those compounds and substances that until recently were not considered xenobiotics and are now increasingly entering the environment in significant quantities and therefore posing a threat to the environment. One of the most important groups is pharmaceuticals and personal care products, as they contain a large number of different chemical compounds that have different effects on the environment into which they are released. In this work, the behavior and stability of two drugs, 0.1 mM solutions of sofosbuvir and oseltamivir, were tested by forced degradation tests: a) alkaline hydrolysis in the presence of a 1.0 M NaOH solution at room temperature for a period of 24 h, b) acid hydrolysis in the presence of a 1.0 M HCl solution at room temperature over a 24-hour period, c) oxidation in the presence of a 30% H2O2 solution at room temperature over a 24-hour period, d) thermal decomposition (neutral hydrolysis) at room temperature, 30 °C, and 40 °C over 168 hours (7 days), and e) photolytic decomposition exposed to UV light at 600 W/m^2 at 25°C over a 6-hour period. Analyses of all excluded samples were performed by HPLC, and the determination methods for both drugs were previously developed and validated. Based on the validation results obtained, both methods met the requirements for all parameters: Linearity with coefficient of determination higher than 0.99, Accuracy with analytical recoveries between 70 and 130%, and Precision with RSD values lower than 10%. Regarding the forced degradation tests, it can be concluded that sofosbuvir and oseltamivir showed satisfactory and expected stability under all tested conditions.