Oral solid dosage forms, due to their mature manufacturing processes and stability, have become the cornerstone of clinical drug therapy. However, fixed dosages, uniform components, and large-scale production may not meet increasingly complex personalized requirements. The emergence of 3D-printed drugs provides a potential solution to this challenge. Drug 3D printing has progressed beyond feasibility verification and is moving toward functional dosage form design. Current research primarily focuses on printability; however, this review integrates printing technology, polymer functionality, structural design, release behavior, and translational requirements, summarizing mainstream printing technologies, including Fused Deposition Modeling (FDM), Direct Ink Writing/Semi-Solid Extrusion (DIW/SSE), Powder Bed Printing (SLS/BJ), and Photopolymerization (SLA/DLP). Polymers are classified according to drug release control functions, illustrating how modulation of porosity, filling density, shell thickness, material partitioning, and spatial drug distribution enables 3D-printed dosage forms with diverse therapeutic functions. These functions include immediate and sustained release, gastric retention, intestinal targeting, and sequential release of multiple components. This review provides guidance for technical selection, structural design, and formulation development of 3D-printed drugs, while highlighting major translational barriers, including limited printable excipients, empirical formulation development, insufficient structure-based release prediction, quality control challenges, and weak clinical evidence. Future progress requires close integration of material, process, structure, and performance, enabling 3D-printed drugs to evolve from individual prototypes into scalable, quality-controllable, and clinically translatable drug delivery systems.