Implantable bioelectronic devices pave the way for novel biomedical applications operating at high spatiotemporal resolution, which is crucial for neural recording and stimulation, drug delivery, and brain-machine interfaces. Before successful long-term implantation and clinical applications, these devices face a number of challenges, such as mechanical and operational stability, biocompatibility, miniaturization, and powering. To address two of these crucial challenges-miniaturization and powering-the development and characterization of an electrophoretic drug delivery device, manufactured inside fused quartz fibers (outer diameter of 125 mu m), which is self-powered by a flexible piezoelectric energy harvester, are reported. The resulting device-the first integration of piezoelectric charging with "iontronic" delivery-exhibits a high delivery efficiency (number of neurotransmitters delivered per charges applied) and a direct correlation between the piezoelectric charging and the amount delivered (number of dynamic bends versus pmols delivered).