I don't personally have asthma but I will give you some information about it.
Inhalers are the main treatment for asthma. However, some side effects do occur in some people. Some of the inhaler drug hits the back of the throat. Sometimes this can cause problems such as thrush in the mouth. This tends to be more of a problem with higher doses of steroid inhalers.Therefore, a spacer device may be advised if you get throat problems, or need a high dose of inhaled steroid.
You can visit this website: http://www.patient.co.uk/health/inhalers-for-asthma