How to Use a Metered Dose Inhaler Correctly

If you live with asthma, your inhaler is one of your most important tools. But up to half of people using a metered dose inhaler (MDI) don't get the full dose into their lungs. The good news? A few small adjustments make a big difference. Whether you use a blue reliever or a preventer, getting your technique right means better symptom control and fewer flare-ups.

Why Your Inhaler Technique Matters

When you press the canister, it releases a fine mist of medicine. If you don't coordinate your breathing with the press, most of it lands on your tongue or throat instead of travelling into your airways. Over time, poor technique means your asthma isn't as well controlled as it could be. You might reach for your reliever more often or wake at night with symptoms. The fix is simple: shake, prime, breathe in slowly and deeply, and hold your breath.

Getting Ready: Priming and Checking Your Inhaler

Before using a new inhaler – or one you haven't used for a while – you need to prime it. Priming means releasing a few puffs into the air to make sure the canister works and the medicine is mixed. Check your patient leaflet, as the number of priming puffs varies. Some need one or two, others four. If you haven't used your inhaler for two weeks or more, prime it again.

Also check the dose counter, if your inhaler has one. When it gets low, order a replacement from your GP or pharmacist. Never use an inhaler past its expiry date. If the canister feels unusually light or the spray seems weak, it may be empty even without a counter.

The Step-by-Step Method for a Metered Dose Inhaler

Follow these steps for every dose. If you use a spacer, skip to the next section – but you still need to shake and prime.

• Shake vigorously for five seconds. This mixes the medicine with the propellant. Do it before every puff, even if taking two in a row.
• Stand or sit up straight. Good posture gives your lungs room to expand.
• Breathe out gently and fully. Don't breathe into the inhaler – just breathe out normally, away from the mouthpiece.
• Place the mouthpiece between your teeth and seal your lips. Make a tight seal so no air escapes. Don't bite down.
• Press the canister once and breathe in slowly and deeply at the same time. Start breathing in just before you press, and keep going for three to five seconds. You may feel a cool sensation or taste the medicine – but don't worry if you don't.
• Remove the inhaler and hold your breath for up to ten seconds. This lets the medicine settle in your airways. If ten seconds is too long, hold as long as you comfortably can, then breathe out slowly.
• Wait about 30 seconds before the next puff. Shake again and repeat. This wait helps the first puff work.

Using a Spacer: A Game-Changer for Many People

A spacer is a plastic chamber that attaches to your inhaler. It makes it much easier to get medicine into your lungs because you don't have to coordinate pressing and breathing at the same time. Spacers are recommended for almost everyone using an MDI, especially for preventer inhalers and for children. They also reduce medicine landing in your mouth, lowering the risk of oral thrush and hoarseness.

To use a spacer: remove the cap, shake the inhaler well, and insert it into the spacer. Put the spacer mouthpiece in your mouth and seal your lips. Press the canister once. Then breathe in slowly and deeply through your mouth, and hold your breath for up to ten seconds. If that's difficult, take five or six normal breaths in and out of the spacer instead – the medicine still reaches your lungs. Clean your spacer monthly with warm soapy water and let it air dry. Don't rub it dry, as static makes medicine stick to the sides.

After You Inhale: Rinsing, Cleaning, and Common Mistakes

If you use a preventer inhaler containing a steroid, always rinse your mouth with water and spit it out after your dose. This helps prevent oral thrush and a sore throat. You don't need to rinse after a reliever, but it won't hurt. Clean your inhaler's plastic actuator weekly: remove the canister, wash the plastic part in warm water, and let it air dry completely before reassembling. Never put the metal canister in water.

Common mistakes to watch out for:

• Not shaking before each puff.
• Forgetting to prime a new or unused inhaler.
• Breathing in too fast – this makes medicine hit the back of your throat.
• Pressing the canister before or after you start breathing in, rather than at the same time.
• Not holding your breath after inhaling.
• Using a preventer without a spacer.
• Not rinsing your mouth after a steroid preventer.

When to Ask for Help

If you're unsure whether your technique is right, ask for a check. Your GP, asthma nurse, or pharmacist can watch you use your inhaler and suggest improvements. Many pharmacies offer a free inhaler technique check – just ask. It's worth reviewing your technique every year, or whenever you get a new inhaler, because bad habits creep in easily. If your asthma symptoms are getting worse despite using your inhaler as prescribed, don't struggle on – book an appointment. Good technique is the foundation of good asthma control, and a five-minute check can make a world of difference.