A clutch assembly with a blocking system for a medical injection device, in which a first ratchet sleeve (3) is mounted on the clutch sleeve (2), the first ratchet sleeve (3) being rotatable in two directions and cooperating with a second ratchet sleeve (4) which is mounted on the first ratchet sleeve (3), the second ratchet sleeve (4) being rotatable only in one direction, the housing (1) has an internal toothed ring (1.1), the first ratchet sleeve (3) has at least one ratchet (3.1), and the second ratchet sleeve (4) has an internal toothed ring (4.1) and at least one ratchet (4.2). The second ratchet sleeve (4) and the housing (1) have blocking means (4.3, 1.2) for preventing the arming of the device when an insufficient volume of the medicament remains in the container, by blocking the rotation of the second ratchet sleeve (4) in relation to the housing (1).