An implantable flow regulator for the infusion of drugs into an animal body from a pressure actuated drug delivery device, such as an implantable infusion pump. The flow regulator comprises a body having a shallow cavity divided into two chambers by a flexible diaphragm. The first of these chambers is a pressure sensing chamber. The other is a valving chamber through which the drug flows, the outlet from that chamber being centrally disposed underlying the diaphragm whereby flexing of the diaphragm in one direction as a result of increased pressure in the other chamber contacts an elastomeric sealing ring around the outlet and closes off the flow path. At least one capillary restrictor is disposed in the flow line between the drug delivery device and flow regulator. The pressure drop across this restrictor governs operation of the flow regulator valve.