The present invention provides an implantable solid polymer delivery composition that can be formulated to release a bioactive agent to an interior body site at a controlled rate over an extended period of time by adjusting the various components of the composition. The controlled delivery of the composition avoids an initial drug spike, resulting in a smooth delivery profile over time. Polymer layers in the composition can be porous and are both biodegradable in water and body enzymes and biocompatible. Methods of making the implantable solid polymer compositions and methods of delivering a bioactive agent at a controlled rate to an interior body site are also provided.