An implantable, refillable, rate controlled drug delivery device is disclosed that includes a base structure having at least a first opening and a second opening, the base structure defining a chamber, a septum covering the first opening and configured to substantially prevent leakage from the first opening to an exterior of the device, a drug delivery tube comprising a first and second distal end, wherein the first distal end of the tube communicates with the chamber through the second opening, and at least one rate-limiting permeable membrane disposed across a passage between the base structure and the second distal end of the drug delivery tube, which membrane passively regulates drug delivery. The drug delivery device is used to provide controlled drug delivery to an internal portion of the body and is advantageously leak-proof and does not rely on a pressure differential to drive the drug from the device.