Implantable pumps and cannulas for them

An implantable pump (100) comprising: a drug reservoir (108), a cannula (120) for conducting liquid from the reservoir; means (112, 124, 134) to drive the liquid from the reservoir through the cannula, characterized by a sensor (148) for monitoring at least one indication that the liquid flows through the cannula parameter; and circuitry (132) to adjust the drive means based on the monitored parameters.