A device for the controlled continuous administration of an active agent to an environment of use is disclosed. The device comprises a body of erodible agent release rate controlling material containing an agent dispersed therethrough; the rate controlling material is a hydrophobic poly(carboxylic acid) having one ionizable carboxylic hydrogen for each 8 to 12 carbon atoms, which material erodes at a controlled and continuous rate over a prolonged period of time in response to the environment by a process of carboxylic hydrogen ionization, thereby releasing the dispersed agent at a controlled rate over a prolonged period of time.