A clutch assembly with a blocking system for a medical injection device, the clutch assembly comprising a clutch sleeve located in a tubular housing, wherein the rotation of the clutch sleeve in a first direction arms the injection device for delivery of a defined dose of a medicament contained in a container and the rotation of the clutch sleeve in a second direction causes delivery of the dose, characterized in that a first ratchet sleeve is mounted on the clutch sleeve, the first ratchet sleeve being rotatable in two directions and cooperating with a second ratchet sleeve which is mounted on the first ratchet sleeve, the second ratchet sleeve being rotatable only in one direction, the housing has an internal toothed ring (1.1), the first ratchet sleeve has at least one ratchet (3.1), and the second ratchet sleeve has an internal toothed ring (4.1) and at least one ratchet (4.2), the toothed rings (1.1, 4.1) have their teeth directed in mutually opposite directions and the ratchets (3.1, 4.2) are directed in mutually opposite directions, the at least one ratchet (3.1) of the first ratchet sleeve cooperates with the toothed ring (4.1) of the second ratchet sleeve, the at least one ratchet (4.2) of the second ratchet sleeve cooperates with the toothed ring (1.1) of the housing, wherein during arming of the device the first ratchet sleeve is stationary in relation to the second ratchet sleeve, the second ratchet sleeve is turned in relation to the housing in said first direction by one tooth of the ring (1.1), and during delivery of a dose the second ratchet sleeve is stationary in relation to the housing while the first ratchet sleeve is turned in relation to the second ratchet sleeve in said second direction by one tooth of the ring (4.1), and wherein the second ratchet sleeve and the housing 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 in relation to the housing. a first ratchet sleeve is mounted on the clutch sleeve, the first ratchet sleeve being rotatable in two directions and cooperating with a second ratchet sleeve which is mounted on the first ratchet sleeve, the second ratchet sleeve being rotatable only in one direction, the housing has an internal toothed ring (1.1), the first ratchet sleeve has at least one ratchet (3.1), and the second ratchet sleeve has an internal toothed ring (4.1) and at least one ratchet (4.2), the toothed rings (1.1, 4.1) have their teeth directed in mutually opposite directions and the ratchets (3.1, 4.2) are directed in mutually opposite directions, the at least one ratchet (3.1) of the first ratchet sleeve cooperates with the toothed ring (4.1) of the second ratchet sleeve, the at least one ratchet (4.2) of the second ratchet sleeve cooperates with the toothed ring (1.1) of the housing, wherein during arming of the device the first ratchet sleeve is stationary in relation to the second ratchet sleeve, the second ratchet sleeve is turned in relation to the housing in said first direction by one tooth of the ring (1.1), and during delivery of a dose the second ratchet sleeve is stationary in relation to the housing while the first ratchet sleeve is turned in relation to the second ratchet sleeve in said second direction by one tooth of the ring (4.1), and wherein the second ratchet sleeve and the housing 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 in relation to the housing.