A drug delivery device is provided. In an embodiment, the device includes a polymeric wall structure which includes a first wall portion and an adjacent second wall portion, wherein the first and second wall portions have been co-extruded to define and bound a drug reservoir space. A drug is contained in the drug reservoir space. The device includes an aperture that is in fluid communication with the drug reservoir space. The first and second wall portions are impermeable to the drug. The first wall portion is water impermeable, and the second wall portion is water permeable and configured to permit water in vivo to diffuse into the drug reservoir space and produce an osmotic pressure for driving release of the drug through the aperture.