Why breathe medicine in?
Most lung diseases live in the airways — the branching tubes that carry air toward the air sacs. If you swallow a pill, the drug must travel through the gut and bloodstream before a small fraction reaches the lung. Inhaling delivers the drug straight to where it is needed, so you can use a much smaller dose with far fewer whole-body side effects. A puff of a reliever can relax tight airway muscle within minutes.
The catch is that the lung is also very good at filtering particles out before they go deep. Only droplets or powder grains of roughly 1–5 microns settle in the small bronchioles; larger ones crash into the throat and are swallowed, smaller ones are breathed straight back out. Every inhaler design is really an answer to one question: how do we get a precise dose of particles of the right size deep into the chest?
Two main families of inhaler
A metered-dose inhaler (MDI), the classic pressurized canister, fires a fixed spray of drug suspended in propellant. It is fast and reliable but needs coordination: you must press and breathe in at the same moment, slowly and deeply. A dry-powder inhaler (DPI) holds the drug as a fine powder and has no propellant — your own breath pulls the powder out, so you must breathe in fast and forcefully to break the powder into fine particles.
- Shake the MDI (if it is a suspension) and remove the cap; sit or stand upright.
- Breathe all the way out, away from the inhaler.
- Seal your lips around the mouthpiece, start a slow deep breath in, and press the canister once at the very start of that breath.
- Keep breathing in slowly, then hold your breath for about 10 seconds to let particles settle.
- Wait about 30 seconds before a second puff; rinse your mouth if the inhaler contains a steroid.
Technique is half the medicine
Studies repeatedly find that a large share of people make at least one critical error with their inhaler. The most common with an MDI is pressing and breathing in at different times; with a DPI it is breathing in too softly. A perfect drug delivered badly behaves like a weak drug. This is why clinicians ask patients to demonstrate their technique rather than just describe it, and why the same person with asthma or COPD may do better on one device family than another.