A metered-dose inhaler (MDI) is a device used to deliver medication directly to the lungs. It contains a pressurized canister that releases a specific dose of medication in aerosol form when activated. MDIs are commonly used for conditions like asthma and chronic obstructive pulmonary disease (COPD). To use an MDI, the user typically shakes the inhaler, exhales fully, and then places the mouthpiece in their mouth. They press down on the canister while inhaling deeply to ensure the medication reaches the lungs effectively. Proper technique is essential for optimal medication delivery.