Pharmaceutics present in the environment are of growing concern for their potential consequences on human and ecosystem health. In long-term monitoring investigations of sewage and surface water samples, diclofenac was identified as one of the most important pharmaceutically active compounds. Pangasius sp. were exposed to determine the lethal concentration (LC50) of diclofenac. The histopathological studies in a fish hepatopancreas sample showed significant changes like nucleation, differentiation, and hepatocytes. The large lesions and infiltration in hepatocytes were distinctly seen due to the toxic effect of diclofenac. In HPLC analysis, the control fish liver tissue showed no significant changes, whereas the diclofenac-exposed fish liver tissue showed a significant peak with a quicker run time. The studies confirmed that the diclofenac compound affects hepatocytes to a noteworthy extent. Therefore, this calls for reduction of diclofenac usage and also to have a checkpoint especially for diclofenac in the pharmaceutical effluent released into the water bodies.