A breath-powered, dry powder inhaler, a cartridge, and a pulmonary drug delivery system are provided. The dry powder inhaler can be provided with or without a unit dose cartridge for using with the inhaler. The inhaler and/or cartridge can be provided with a drug delivery formulation comprising, for example, a diketopiperazine and an active ingredient, including, peptides and proteins such as insulin, oxyntomodulin and glucagon-like peptide.