Abstract: The present invention provides an inhaler assembly for providing medications in aerosol form to animals, especially equines. The inhaler assembly comprises a holder adapted to retain at least two diffusion canisters containing either substantially the same or different drug formulations. The canister holder has an outlet in communication with the inlet of a spacer. The spacer, in turn, has an outlet in communication with a mask such that, in use, medication from at least one of the canisters can be dispensed into the spacer for inhalation in aerosol form via the mask.