Adsorption properties of graphene oxide (GO) and its organo-modified analog (GO-HDTMA), treated with the hexadecyltrimethylammonium (HDTMA) cationic surfactant, were evaluated for the removal of persistent pharmaceutical products (PPs): an anionic diclofenac (DCF) anti-inflammatory, a cationic metoprolol (MTP) beta-blocker, and a nonionic sulfamethoxazole (SMX) antibiotic. Adsorption isotherms, fitted by Langmuir and Freundlich models, together with FTIR data, demonstrate that both GO and GO-HDTMA are effective adsorbents for DCF. The adsorption is primarily governed by both π–π and van der Waals interactions, leading to saturation of the accessible C sp² carbon domains at a maximum uptake of 4.2 mmol g⁻¹. In contrast, due to its cationic nature, MTP is not removed using GO-HDTMA, while it is effectively adsorbed at about 0.5 mmol g⁻¹ for GO via electrostatic attractive forces. SMX is adsorbed by both materials, although its uptake remains limited on GO. The presence of hydrophobic domains in GO-HDTMA enhances SMX adsorption through weak intermolecular interactions. These results highlight the tunability of GO-based hybrid materials and their potential for the selective removal of a large spectrum of emerging pharmaceutical contaminants.