Coupling mechanism for a vehicle anti-roll bar comprising a first piece able to be fixed to a first half-bar, a second piece able to be fixed to a second half-bar, the second piece being so arranged as to be moveable in rotation about an axis of rotation A relative to the first piece. The mechanism includes at least one elastically deformable elongate element coupled to the first and second pieces so that relative rotation of the first and second pieces about the axis of rotation A causes elastic flexion deformation of the at least one elongate element, the mechanism including an actuator able to position the at least one elongate element in a first state in which the said at least one elongate element presents a first flexion stiffness for the said elastic flexion deformation, and a second state in which the said at least one elongate element presents a second flexion stiffness for the said elastic flexion deformation.