A mechanism for administering a drug in the form of a powder or aerosol mainly used by patients with ASTHMA. Inhalers are basically of two types: aerosol, and dry-powder inhaler. The former delivers the drug as an aerosol spray when the patient presses the top of the canister containing the drug; the latter works by putting a drug capsule in the end of the chamber and, when the patient presses the top, the capsule is pierced and the drug released. A variety of ‘spacing devices’ are available for use with pressurised (aerosol) inhalers, providing metered doses. The space introduced between the inhaler and the mouth reduces the velocity of the aerosol and thus the impact it has on the throat. More time is thus allowed for evaporation of the propellant, with a greater concentration of drug particles being inhaled into the air tubes and lungs. Devices with larger spacing devices and a one-way valve are very effective and particularly useful for children and patients needing higher doses of the drug. (See INHALANTS; NEBULISERS.)