Which medication is commonly used to treat asthma?

Ventolin HFA, which contains the active ingredient albuterol, is a commonly used medication for the treatment of asthma. Albuterol is a bronchodilator, which means it works by relaxing the muscles in the airways, resulting in widened air passages and improved airflow to the lungs. This makes it particularly effective during acute asthma attacks or for quick relief of asthma symptoms.

While Allegra is an antihistamine that treats allergies, Flonase is a nasal spray used for allergic rhinitis and does not primarily treat asthma, although it may help with related conditions. Glucophage is a medication for managing type 2 diabetes and does not have any application in treating asthma. Therefore, Ventolin HFA stands out as the correct answer for treating asthma specifically.