An inhaler for holding a canister (2) of medicament. The canister (2) has a mount (26) secured thereto mounting an indication member (41) movable slidably from a first state to a second state. A ratchet arrangement (41a, 42) is provided between the mount (26) and the indication member (41) to make the movement irreversible. The inhaler has a catch (49) for moving the indication member from the first state to the second state on removal of the canister (2) from the inhaler. An electrical switch contact (48) detects the state of the indication member (41), thereby providing an indication of whether the canister (2) has been used before. An LCD display is controlled in response to the detection.