Two problems in one disease
In asthma, two things happen at once. The ring of muscle around each airway squeezes shut — that is the sudden, frightening wheeze. And the airway lining is chronically inflamed and swollen, which keeps the airways twitchy and narrow even between attacks. Two problems mean two jobs: relax the muscle now, and calm the inflammation over time. Mixing these two roles up is the single most common mistake patients make with their inhalers.
The reliever. A bronchodilator relaxes the airway muscle. The classic one is a beta-2 agonist — it is an agonist (an activator) at the beta-adrenoceptor on airway muscle, and switching that receptor on tells the muscle to let go. A short-acting one (the "blue inhaler") opens the airway within minutes; it is the rescue puff for an attack.
The preventer. An inhaled corticosteroid does nothing for a sudden wheeze, but taken every day it quietly heals the inflamed lining so attacks become rarer and milder. This is why a preventer must be used even when you feel well — it is working on the problem you cannot feel. For some people a leukotriene antagonist tablet adds extra control by blocking another inflammatory messenger.
Why we breathe the drug in
These drugs are delivered by the inhalation route for a beautiful reason: it sends the medicine straight to the airways where it is needed, using a tiny dose, so very little reaches the rest of the body. That gives fast action and far fewer whole-body side effects than swallowing the same drug. The trade-off is technique — if the puff and the breath are not coordinated, most of the dose lands in the mouth instead of the lung.
One more idea worth holding: selectivity. A beta-2 agonist is designed to prefer the beta-2 receptors of the airways over the beta-1 receptors of the heart. The preference is good but not perfect, so a big or frequent dose can still cause a fast heartbeat and shaky hands — a hint that you are over-relying on the reliever and your asthma control needs review. In COPD an antimuscarinic bronchodilator is often added, opening airways through a completely different nerve pathway.