Dosages of inhaled insulin are controlled within a narrow range by controlling the total volume of air inhaled by a patient. By repeatedly delivering aerosolized insulin with the same total inhaled volume of air, the amount of insulin delivered to the patient each time is consistent. A device for delivering insulin by inhalation is disclosed which device comprises a means for measuring inhaled volume and for halting inhalation at a pre-determined point. The device also comprises an adjustable means for applying various amounts of force to a container of formulation to expel different amounts of drug from the container based on the force applied.