Embodiments of the present invention utilize a closed-loop feedback control system to ensure accurate drug delivery. This control system may, for example, utilize a flow sensor to measure the volume of delivery and an intelligent control algorithm to anticipate and compensate for overdoses and underdoses. Feedback control systems in accordance herewith can be applied to any piston- or plunger-driven pump system utilizing sensors that measure flow directly or indirectly. In some embodiments, adjustments are made based on the flow “tail” that occurs in a piston- or plunger-type pump as relaxation of the plunger material continues to push fluid out of the drug reservoir; this residual flow eventually ceases after the plunger returns to its natural state.