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 two types of inhalers:

• A metered-dose inhaler (MDI) is a small canister that contains medicine in an aerosol form. When the person triggers the puff of medicine, he or she 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 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 dry powder inhaler works may depend on how well a person inhales. A dry powder inhaler should not be used with a spacer.