Using a metered dose inhaler (MDI) correctly means shaking it, breathing in slowly as you press the canister, and holding your breath for up to 10 seconds so the medication reaches deep into your lungs. It sounds simple, but studies consistently show that most people make at least one mistake that reduces how much medicine actually gets where it needs to go. Here’s how to get the full dose every time.
Step-by-Step Technique Without a Spacer
Remove the cap and hold the inhaler upright with your index finger on top of the canister and your thumb supporting the bottom of the mouthpiece. Shake the inhaler well for about 5 seconds. This mixes the medication evenly with the propellant inside so each spray delivers a consistent dose.
Breathe out fully, away from the inhaler. This is one of the most skipped steps: a systematic review of U.S. studies found that roughly 2 out of 3 patients fail to exhale before inhaling their medication. Emptying your lungs first creates more room for the medicated air to travel deep into your airways.
Place the mouthpiece between your teeth and close your lips around it to form a seal. Begin breathing in slowly and deeply through your mouth. As you start that breath, press down once on the top of the canister to release one puff. The timing here is critical. You need to coordinate the press with the start of your inhalation so the spray rides the airflow into your lungs rather than coating the back of your throat.
Continue inhaling slowly and steadily until your lungs feel full. For an MDI, slow and deep is the rule. Clinical guidance recommends an inhalation flow rate under 90 liters per minute, which in practical terms means a gentle, steady breath that takes about 3 to 5 seconds. This is the opposite of a dry powder inhaler, which requires a fast, forceful breath. About 1 in 3 patients inhale too quickly, which causes more medication to land in the mouth and throat instead of the lungs.
Once your lungs are full, remove the inhaler from your mouth and hold your breath for about 10 seconds (or as long as is comfortable). This pause gives the tiny medication particles time to settle onto your airway surfaces. Around 2 in 5 patients skip or cut short the breath hold, which directly reduces how much medicine is absorbed.
Breathe out gently through your nose or pursed lips. If you need a second puff of the same medication, wait about 1 minute before repeating the full process, starting with shaking the inhaler again.
Using a Spacer
A spacer (sometimes called a valved holding chamber) is a tube that attaches between the inhaler and your mouth. It holds the medication cloud in a small chamber for a few seconds, which solves the biggest problem most people have: coordinating the press of the canister with the start of a breath. With a spacer, you don’t need perfect timing. You press the canister, the medication suspends inside the chamber, and then you inhale at your own pace.
Spacers also filter out larger droplets that would otherwise stick to the back of your throat, so more of the fine particles reach your lower airways. The technique is identical to using an MDI alone, with two changes: attach the spacer to the mouthpiece first, and after pressing the canister, begin breathing in slowly from the spacer within a few seconds. Some valved holding chambers make a whistling sound if you’re inhaling too fast, which acts as a built-in guide for pacing your breath.
If your spacer has a mask (common for young children), press it firmly against the face to create a seal and allow 5 to 6 breaths to empty the chamber completely.
Priming a New or Unused Inhaler
Before you use a brand-new inhaler for the first time, or if you haven’t used it in several days, you need to prime it. Priming means spraying a few puffs into the air (away from your face) to clear the valve and ensure the next press delivers a full, accurate dose. The number of priming sprays varies by product, typically between 1 and 4, so check the label or patient insert that comes with your specific inhaler. Most manufacturers recommend re-priming if the inhaler hasn’t been used for 7 to 14 days.
The Most Common Mistakes
A meta-analysis of U.S. studies covering over 1,100 patients identified the errors that happen most often, in order of frequency:
- Not exhaling before inhaling (about 66% of patients). Skipping this step means your lungs are already partially full, leaving less space for medicated air.
- Not holding the breath long enough (about 42%). Even 5 seconds is better than none.
- Inhaling too fast (about 39%). A quick, sharp breath sends the medication crashing into the back of your throat. Think of it as sipping air through a straw, not gasping.
- Forgetting to shake the inhaler (about 34%). The medication settles inside the canister between uses, so an unshaken puff may contain mostly propellant.
The single biggest category of errors involves hand-breath coordination: pressing the canister at the wrong moment relative to the inhalation. If you consistently struggle with the timing, a spacer effectively eliminates this problem.
Rinsing Your Mouth After Steroid Inhalers
If your inhaler contains a corticosteroid (used for long-term inflammation control, not quick relief), rinse your mouth with water and spit it out after every use. Residual steroid on the tongue, cheeks, and throat can cause oral thrush, a white fungal overgrowth, and a hoarse or sore voice. Rinsing also reduces the small amount of medication that might be swallowed into your system. Despite this being a standard recommendation, nearly one-third of patients either skip rinsing or do it incompletely. A quick swish-and-spit takes a few seconds and prevents problems that otherwise build up over weeks.
How to Know When Your Inhaler Is Empty
This is trickier than it sounds. An MDI canister can feel like it has something left even when it’s well past its labeled number of doses, because the propellant lingers after the active medication runs out. In one study, nearly 74% of patients judged an empty inhaler to be full or partially full. You could be pressing the canister and inhaling nothing but propellant without realizing it.
The most reliable method is dose counting. Note the total number of doses printed on the canister (commonly 60 or 200), then track how many puffs you’ve used, including priming sprays. Some newer inhalers have a built-in dose counter on the back of the device, though even these aren’t foolproof: in one audit, 18% of inhalers with dose counters had already been used past empty. If your inhaler doesn’t have a counter, write the start date on the canister with a marker and calculate when you’ll hit the labeled number of doses based on your daily use.
The old “float test,” where you drop the canister in water to see if it sinks or floats, is unreliable and no longer recommended. It doesn’t accurately reflect remaining medication, and submerging the canister can damage the valve.