Since asthma is a problem that starts in the lungs, most asthma medications are inhaled into the lungs to treat the problem at the source. Handheld inhalers—the most common delivery method for asthma medications—work more quickly because they send the medication directly into the lungs and cause fewer side effects than some liquid versions of medication, which are swallowed.

There are two types of inhalers used to treat asthma: metered-dose inhalers (MDI) and dry powder inhalers. MDIs, which are often used with devices called spacers (tube-like attachments that make it easier for children to use an inhaler), contain medication in aerosol form. Dry powder inhalers, which are not compatible with spacers, store the medication in powder form.