Antioxidant cytoprotective properties of mexidol have been studied under the influence of argon and helium gas-discharge cold plasma of atmospheric pressure on Paramecium caudatum cell culture. It has been shown that mexidol exhibits strong antioxidant properties and practically completely eliminates the negative effects of oxidative stress, retaining almost 100% of the initial number of cells. The data obtained demonstrate a wide range of behavioral responses of cells of Paramecium caudatum, which confirms their practical value as model objects for pharmacological and toxicological studies, and the use of gas-discharge cold plasma makes it possible to exclude the direct oxidative effect of hydrogen peroxide (the standard model of oxidative stress) on the studied drugs and to increase the reliability of toxicological studies.