The main aim of this study was to examine the effect of polypropylene (PP), poly(ethylene terephthalate) (PET), and poly(lactic acid) (PLA) microplastics (MPs) on the photolytic degradation of a mixture of seven commonly used pharmaceuticals under simulated solar irradiation (SSL).The target mixture included four common antibiotics (metronidazole, trimethoprim, indomethacin, isoniazid), two non-steroidal anti-inflammatory drugs (diclofenac, ketoprofen), and one antihypertensive drug (valsartan).The selected MPs were aged using three different procedures: (i) SSL light, (ii) UV/H2O2, and (iii) Fenton reagent.The effect of MPs mass concentration was examined using only the pristine MPs, while the aging effect was evaluated for the three different aged MPs for each polymer type.The results demonstrated that the presence of MPs generally accelerates the photolytic degradation of the drugs, and increasing their concentration further enhances the reaction rate.Aging of the MPs also appeared to enhance the photodegradation of the selected pharmaceuticals.Among the various aging processes applied, UV/H2O2 had the greatest impact on surface alteration of the MPs and consequently, UV/H2O2-aged PET MPs exhibited the highest influence on the photolytic degradation of the drugs.To gain a deeper understanding of the mechanism behind the photolytic degradation of the examined pharmaceuticals, a systematic characterization of pristine and aged MPs was conducted using Fourier transformed IR spectroscopy (FTIR), XPS, and SEM-energy dispersive X-ray spectroscopy (SEM-EDX) techniques, which detected the formation of oxygen containing groups on the MPs' surfaces.Finally, scavenger experiments were also conducted to explore the formation and role of reactive oxygen species (singlet oxygen, superoxide anions, and hydroxyl radicals) in the degradation of the target compounds