The invention relates to a powder formulation for administration by inhalation comprising an active substance and a pharmaceutically acceptable excipient, which composition has the form of a physical mixture and comprises from 5 to 25 wt. % of the excipient, and wherein the active substance has a particle size distribution of from 0.5 to 10 .mu.m, and wherein the excipient has a particle size distribution of from 15 to 500 .mu.m.