A dry powder inhaler for pulmonary or nasal use, comprising at least an inhaler body and a cartridge with one or more compartments each containing one dose of a drug. The compartment has holes to admit air and holes to deliver powder, which, in use, communicate with an inhalation channel in the inhaler body. To prevent the powder from leaking through the compartment holes before use, the air admission holes are of reduced dimension, thereby blocking or hindering powder exit under the force of gravity. When the cartridge is inserted inside the inhaler body, all its holes can be blocked. By sliding the cartridge in relation to the body until the inhalation position is reached, the holes come into in fluid communication with one another and with the inhalation channel, thereby allowing a flow of air to disperse and entrain the dose through the mouthpiece. Five embodiments are disclosed.