In today's world, the use of pharmaceuticals is on the rise. After consumption, pharmaceuticals are excreted from the bodies of humans and animals as a mixture of metabolites and partially unchanged active substances, thus entering the environment. Traditional wastewater treatment plants do not remove such small molecules from wastewater. A significant problem arises with antiparasitic drugs widely used in veterinary medicine. They have complex chemical structures, are poorly water-soluble, prone to crystallization, and persist in the environment, accumulating in water treatment systems. On the other hand, pesticides, especially herbicides in agriculture, are increasingly used and end up in the environment, particularly in nearby streams and rivers. Pesticides are mostly water-soluble and easily find their way into groundwater. The harmful impact of both pharmaceuticals and pesticides is partially understood, but the influence of their degradation and transformation products that occur during metabolic processes in organisms or under the influence of photolysis and hydrolysis is not well-defined for these compounds, which also end up in the environment. Therefore, it is necessary to monitor these compounds in the environment, both before and after wastewater treatment, using appropriate analytical methods. A special case is the activated sludge generated during wastewater treatment. Many wastewater treatment plants employ conventional biological methods with activated sludge. In such processes, activated sludge becomes an output and potentially hazardous product that needs to be managed. Therefore, it must be analyzed for the presence of dangerous substances before disposal. This study focused on monitoring antiparasitic drugs albendazole, mebendazole, and febantel, as well as the pesticide thiacloprid in activated sludge using chromatographic methods after microwave-assisted solvent extraction. The study involved optimizing the microwave-assisted extraction procedure for samples and determining validation parameters with an emphasis on method selectivity.