The asthma inhalers can be broadly classified into two types- the metered dose inhalers and the dry powder inhalers. Out of these two the most frequently used asthma inhaler is the metered dose inhaler.

Metered dose inhalers
These types of inhaler contain the drugs in the form of a formulation which is kept inside a canister at high pressure along with a liquefied propellant. These have the main function of directing the medication in the form of aerosol into the patient's lungs. When the mouthpiece is kept inside the mouth and pressure is applied on the canister a measured value of medication is released in patient's mouth. That is why they are called metered dose inhalers.

Dry Powder inhalers.
These inhalers have the drugs in the form of a powder. These drugs present in the inhalers can be inhaled into the lungs directly using the patient's own breath. The average cost of this inhaler is more than the metered dose inhalers. Also another major disadvantage of these inhalers is that during an attack, one may not be able to produce adequate airflow to draw in the medication. But these inhalers are more environment friendly then their previous counterpart as metered dose inhalers involve the usage of aerosols.