The way an asthma inhaler works depends on the type of device being used.

Metered Doses

In the case of a metered dose inhaler, a pressurized mini-canister of prescribed medication fits snugly into a plastic, boot-shaped receptacle. At regular, recommended intervals, the patient places the small open portion of the device in their mouth and then presses down on the button at the other the contraption, releasing a set amount of gaseous medicine into their system.

Some metered dose inhalers are triggered simply by the person breathing in, rather than having to press down on a button to release the medication. Other dispensers have counters that keep track of how many doses have been dispensed and, by default, how many are still left in the canister.

Spacers, Dry Powder

Some asthma inhalers have the additional feature of what's called a spacer. This separate compartment acts as a bridging, holding compartment between the canister and the patient, making it easier to breathe in the medication. Rather than the substance being shot directly into a person's mouth, it is "caught" first and thus made more static, for absorption.

Another type of inhaler, known as the "dry powder" model, releases medication only when the user takes deep, short breaths. The patient triggers the action through their breathing pattern rather than by pressing down on a button, Models in this line of inhaler include the dry powder tube inhaler, the single-dose powder disk inhaler, and the multiple dose powder inhaler.

Over-the-Counter

The only asthma inhaler that is sold over-the-counter in the United States is the Primatene Mist. Unfortunately, at least for those patients who have come to appreciate the convenience of getting one without a prescription slip, these devices are to be discontinued at the end of 2011.

As part of an international agreement to phase of chlorofluorcarbons (CFCs), the U.S. is taking this device off the market because it relies on CFCs. Many other types of asthma inhalers have circumvented the ban by replacing the CFCs with hydrofluoroalkane.