A powder for use in a dry powder inhaler comprises: i) a fraction n of fine particle size constituted by a mixture of physiologically acceptable excipient and an additive; ii) a fraction of coarse particles; and iii) at least one active ingredient. The powder is suitable for efficacious delivery of active ingredients into the low respiratory tract of patients suffering from pulmonary diseases such as asthma. In particular, the invention provides a formulation to be administered as dry powder for inhalation which is freely flowable, can be produced in a simple way, is physically and chemically stable and capable of delivering accurate doses and/or high fine particle fraction of low strength active ingredients by using a high- or medium resistance device.