A drainage valve (1) intended to be implanted and to drain the cerebrospinal fluid, comprising: - a body (2) defining a chamber (3) into which there open an inlet port (5) and an outlet port (6), - a stopper (11) capable of at least partially, or indeed completely, closing off the inlet port (5), - a resilient return member (13) exerting a resilient push force on the stopper (11) towards the inlet port in order to open or close the port, - a rotor (8) housed in the chamber, able to rotate about an X-axis pivot and comprising a cam track (19) on which the resilient return member (13) rests such that the force exerted by the resilient return member (13) on the stopper (11) is modified by the rotation of the rotor (8).
