A device for administering an active substance comprises a multi-chamber carpule having a bypass in one wall and at least one first chamber with a solid active substance and a second chamber with a solvent for the active substance, the second chamber being delimited by a first plug arranged distally in the multi-chamber carpule and a second plug arranged proximally therein a mixing element is rotatably mounted about a rotational axis in relation to the housing and can be rotated about the rotational axis in a rotational direction in order to mix the active substance and the solvent and a first detent device is provided on the device such that, after the mixing operation, an axial displacement of the distal end of the second plug in relation to the wall of the multi-chamber carpule is blocked in the proximal direction by means of the distal end of the bypass.
