Pharmaceutical residues are a result of human activities and are increasingly recognized as environmental contaminants that pose significant risks to aquatic ecosystems. There are many well-known pathways (agricultural runoff, veterinary use, human excretion, etc.) for the entry of these pharmaceuticals into the aquatic environment, and among them, the inability to remove these biologically active compounds from wastewater treatment plant (WWTP) effluents is becoming increasingly significant in the context of societal evolution. Once introduced, pharmaceuticals persist at low concentrations, exerting sub-lethal effects that disrupt the physiological processes of aquatic organisms. Among these effects, oxidative stress (OS) has gained attention as a key mechanism that is induced by pharmaceutical toxicity, serving as a sentinel indicator of homeostatic disturbance. Thus, studying OS biomarkers in fish is crucial for understanding the extent of pharmaceutical pollution, as these biomarkers provide early warning signals of environmental stress and help assess sub-lethal impacts on aquatic organisms. Their application, correlated with other eco-physiological investigations, can improve ecological risk assessments. In this context, this review explores the role of OS biomarkers by assessing the effects of pharmaceutical contaminants on fish. It highlights the utility and limitations of these biomarkers for environmental monitoring, while also identifying key research gaps—particularly regarding long-term ecological consequences.

Human pharmaceutical residues are increasingly recognized as environmental contaminants that pose significant risks to aquatic ecosystems. This review focuses on the oxidative stress induced in fish by these pharmaceutical residues. Pharmaceuticals, including antidepressants, anti-inflammatories, and other widely used medications, enter aquatic ecosystems through multiple pathways, most notably through their use in human and veterinary medicine, the subsequent metabolic excretion via urine and feces, and wastewater treatment plant effluents. These substances, often only partially removed during water treatment, persist in the environment and pose potential risks to aquatic organisms, impacting water quality and ecosystem health. Upon exposure, fish exhibit oxidative stress responses characterized by the overproduction of reactive oxygen species (ROS) and subsequent damage to cellular components such as lipids, proteins, DNA, and RNA. This review summarizes current research on the oxidative stress (OS) responses of various fish species to environmental concentrations of pharmaceuticals. It explores the mechanisms underlying OS, identifies the specific pharmaceuticals involved, and discusses these responses' physiological and ecological implications.