Medication inhaler for delivering a gaseous therapy to a patient comprising a housing, a top cover fixed to the housing and an inner compartment arranged between said housing and said top cover, and wherein: - the housing comprises a hollow chamber with an exit orifice, and the top cover comprises an outlet, said exit orifice of the hollow chamber and said outlet of the top cover being in fluid communication with the inner compartment, - a venting channel comprising an entry port and a venting port, is in fluid communication with the inner compartment via the entry port and further with the atmosphere via the venting port, and - a one-way valve is arranged in the inner compartment and configured for allowing gas to circulate: i) from the hollow chamber of the housing to the outlet of the top cover, when the patient inhales gas, and ii) from the outlet of the top cover to the venting channel, when the patient exhales gas, wherein the venting channel comprises a mobile element that moves into said venting channel in the direction of the venting port, said mobile element being retained in the area of the venting port and visible from the outside through said venting port, when the patient exhales gas through the outlet of the top cover, thereby providing a visual feedback system allowing to immediately know from the outside, whether said patient is breathing gas, characterized in that: - the mobile element has a spherical or cylindrical shape, - at least a portion of the venting channel and the mobile element are arranged into a removable cassette having an elongated arcuated shape, and - the removable cassette further comprises an inner passage with an inlet and an outlet, said inner passage forming at least a part of the venting channel. - the housing comprises a hollow chamber with an exit orifice, and the top cover comprises an outlet, said exit orifice of the hollow chamber and said outlet of the top cover being in fluid communication with the inner compartment, - a venting channel comprising an entry port and a venting port, is in fluid communication with the inner compartment via the entry port and further with the atmosphere via the venting port, and - a one-way valve is arranged in the inner compartment and configured for allowing gas to circulate: i) from the hollow chamber of the housing to the outlet of the top cover, when the patient inhales gas, and ii) from the outlet of the top cover to the venting channel, when the patient exhales gas, wherein the venting channel comprises a mobile element that moves into said venting channel in the direction of the venting port, said mobile element being retained in the area of the venting port and visible from the outside through said venting port, when the patient exhales gas through the outlet of the top cover, thereby providing a visual feedback system allowing to immediately know from the outside, whether said patient is breathing gas, characterized in that: - the mobile element has a spherical or cylindrical shape, - at least a portion of the venting channel and the mobile element are arranged into a removable cassette having an elongated arcuated shape, and - the removable cassette further comprises an inner passage with an inlet and an outlet, said inner passage forming at least a part of the venting channel. i) from the hollow chamber of the housing to the outlet of the top cover, when the patient inhales gas, and ii) from the outlet of the top cover to the venting channel, when the patient exhales gas, - the mobile element has a spherical or cylindrical shape, - at least a portion of the venting channel and the mobile element are arranged into a removable cassette having an elongated arcuated shape, and - the removable cassette further comprises an inner passage with an inlet and an outlet, said inner passage forming at least a part of the venting channel.