An inhaler is a handheld device that delivers medicine in a measured dose while a person inhales. Inhalers are used in respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD).

Inhaled medicine may work faster than oral medicines to relieve symptoms such as wheezing and spasms in the bronchial tubes, because the inhaler allows the medicine to go directly to the lungs. Inhaled medicine usually causes fewer side effects than oral medicine.

There are three types of inhalers:

• A metered-dose inhaler (MDI) is a small canister that contains medicine in an aerosol form. A person triggers a puff of medicine and inhales. The device measures a specific amount of medicine to be released in each puff. MDIs are often used with spacers, which serve as a holding chamber for the medicine. A spacer increases the amount of medicine going to the lungs and can help people who have problems getting the correct timing when using an inhaler.
• A dry powder inhaler (DPI) contains medicine in a dry powder form. The person breathes in sharply to inhale the medicine. Unlike using an MDI, no coordination between triggering the medicine and inhaling is needed. But how well the DPI works may depend on how well a person inhales. A DPI should not be used with a spacer.
• A soft mist inhaler (SMI) releases medicine in a fine mist. The medicine comes out slowly and lasts longer in the air than the medicine in an MDI. An SMI has a dose counter, so you can see how many doses you have left to use. The device will lock itself after all the medicine has been used. You do not need to shake the SMI before using.