Programmable agent delivery system

A delivery system for delivering a beneficial drug at a controlled rate to a biological environment, wherein the delivery system is comprised of:

• (a) a reservoir comprising a first surface and a second surface, which reservoir is dimensioned for use and retention in a biological environment, the reservoir comprising a polymeric formulation that is pervious to the passage of drug;
• (b) a beneficial drug in the reservoir;
• (c) a first wall occluding the first surface of the reservoir, the first wall essentially-free of drug and impervious to the passage of drug;
• (d) a second wall occluding the second surface of the reservoir, the second wall comprising a polymeric formulation substantially impervious to the passage of an osmotically effective solute;
• and (e) an osmotically effective solute in the second wall.