Implantable medical devices and treatment methods are provided, particularly for use in the bladder. The device is configured for retention in the bladder for at least a portion of the drug delivery period and includes at least one biodegradable component such that following a biodegradation at a selected time, the retention function is lost and the device or portions thereof are resorbed and/or excreted. The method may include deploying into the bladder of a patient a device having a device structure housing a drug formulation comprising at a drug; releasing drug from the device structure into the bladder; and then, changing the composition of urine in the bladder, e.g., by altering the pH, to trigger degradation of at least part of the device structure to enable the device structure or parts thereof to be excreted from the bladder.