Embodiments herein relate to an implantable device comprising a casing, a semi-permeable membrane plug at or near a first end of the casing, a piston, beads, and an opening for release of the beads from the implantable device within a body of a human or an animal; wherein the implantable device is configured to be implanted within the body of the human or the animal during delivery of the beads into the body of the human or the animal; wherein the beads comprise a core and a shell with the core being enclosed by the shell and the beads contain a drug; and wherein the implantable device is configured to produce a desired flow rate of elution of the drug from the implantable device when the implantable device is implanted within the body of the human or the animal.