Metered dose inhalers (MDIs) contain an active drug and propellant that are packed under pressure. Upon activation, an exact amount of the drug is released from the container through a metered valve. MDIs are commonly used to treat asthma, COPD, and heart diseases. They provide portability and convenience as patients can carry and use them immediately for relief from symptoms. However, some patients experience discomfort from the cold propellant spray.