There is described a medicament delivery device which comprises a medicament reservoir, a medicament delivery passage and a metering member adapted to transfer a measured dose of medicament from the medicament reservoir to the delivery passage characterized in that the device is provided with a moisture proof barrier. The medicament delivery device is especially suited for use as an inhaler. There is therefore also described an inhaler which provides improved airflow for the dispersion of medicament, and a method of treating patients suffering from a respiratory disorder.