A portable inhaler comprising a ratchet mechanism, the ratchet mechanism comprising: - a ratchet ring rotatable about an axis relative to a chassis, with a general direction of rotation determined by teeth of the ratchet mechanism, wherein the ratchet ring has a first set of teeth arranged regularly around the ratchet ring and protruding in a first axial direction from the ratchet ring and a second set of teeth arranged regularly around the ratchet ring and protruding in a second opposite axial direction from the ratchet ring; and - the chassis which has a third set of teeth arranged regularly and protruding in the second axial direction and generally opposed to the first set of teeth, and a fourth set of teeth arranged regularly and protruding in the first axial direction and generally opposed to the second set of teeth wherein: - each tooth protruding in the first axial direction or the second axial direction has a leading edge and a trailing edge with respect to the general direction of rotation of the ratchet ring, - the trailing edge on each tooth of the first set of the teeth and the second set of teeth is oriented in the axial direction of protrusion and the leading edge on each tooth of the first set of teeth and the second set of teeth is angled towards the trailing edge with respect to the axial direction of protrusion, and - the leading edge on each tooth of the third set of teeth and the fourth set of teeth is oriented in the axial direction of protrusion and the trailing edge on each tooth of the third set of teeth and the fourth set of teeth is angled towards the leading edge with respect to the axial direction of protrusion. - a ratchet ring rotatable about an axis relative to a chassis, with a general direction of rotation determined by teeth of the ratchet mechanism, wherein the ratchet ring has a first set of teeth arranged regularly around the ratchet ring and protruding in a first axial direction from the ratchet ring and a second set of teeth arranged regularly around the ratchet ring and protruding in a second opposite axial direction from the ratchet ring; and - the chassis which has a third set of teeth arranged regularly and protruding in the second axial direction and generally opposed to the first set of teeth, and a fourth set of teeth arranged regularly and protruding in the first axial direction and generally opposed to the second set of teeth - each tooth protruding in the first axial direction or the second axial direction has a leading edge and a trailing edge with respect to the general direction of rotation of the ratchet ring, - the trailing edge on each tooth of the first set of the teeth and the second set of teeth is oriented in the axial direction of protrusion and the leading edge on each tooth of the first set of teeth and the second set of teeth is angled towards the trailing edge with respect to the axial direction of protrusion, and - the leading edge on each tooth of the third set of teeth and the fourth set of teeth is oriented in the axial direction of protrusion and the trailing edge on each tooth of the third set of teeth and the fourth set of teeth is angled towards the leading edge with respect to the axial direction of protrusion.