Pharmaceutical effluents are increasingly recognised as significant contributors to environmental antibiotic contamination, creating persistent hotspots for antimicrobial resistance development. Unlike therapeutic exposures, these effluents often expose microbes to chronic, sub-inhibitory antibiotic concentrations that shape bacterial adaptation rather than induce immediate cell death. Pseudomonas aeruginosa, a metabolically versatile opportunistic pathogen, exemplifies the public health risks associated with such exposure. This review synthesises open-indexed evidence on how sub-minimum inhibitory concentration (sub-MIC) antibiotics from pharmaceutical discharge can promote biofilm-mediated resistance in P. aeruginosa. Biofilms, structured microbial communities encased in a self-produced matrix, provide a protective environment that limits antibiotic penetration and fosters metabolic heterogeneity. Under sub-MIC exposure, P. aeruginosa biofilms exhibit enhanced formation, altered gene expression, and increased persistence of tolerant and resistant subpopulations. Repeated low-dose antibiotic challenge not only remodels bacterial behaviour but also selects for heritable resistance traits, especially within biofilm-associated cells. Evidence indicates that industrial effluents containing mixtures of antibiotics can maintain selective pressure in aquatic environments, facilitating the survival and propagation of resistant strains. Moreover, the capacity of biofilms to act as reservoirs for resistance genes amplifies their impact on both environmental and clinical settings. Understanding the interplay between pharmaceutical pollution, sub-inhibitory antibiotic levels, and biofilm biology is crucial for mitigating the spread of resistance. This review underscores the urgent need for improved waste management, environmental monitoring, and policy interventions to address the escalating threat of antibiotic resistance driven by pharmaceutical effluents.