A flow regulator (19, 208, 308, 408) may be used in a drug delivery system 10. The regulator includes a chamber that is divided by a diaphragm (111, 211, 311, 411) into a first and second subchamber. A third subchamber is in fluid communication with the first subchamber. A valve (26, 217, 317, 417) is operatively connected to the diaphragm, wherein pressure differences between the first subchamber and second subchamber result in movement of the diaphragm and movement of the diaphragm controls operation of the valve. A flow restrictor (116, 216, 316, 416) is in fluid communication between the first and second subchambers. Flow of a drug (11, 101) is thereby regulated.
