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 . <EOS>