The use of magnesium stearate (I) in dry powder formulations for inhalation to improve resistance to moisture is new. Independent claims are also included for: (1) the use of magnesium stearate to reduce the effect of invasive moisture on the fine particles in dry powders for inhalation； and (2) dry powder formulations for inhalation comprising: (a) an inactive carrier of non-inhalant particle size； (b) a pharmaceutically active agent in the form of a salt or ester of inhalant particle size； and (c) 0.25-1 wt.% of magnesium stearate.
