Sheikh `Abd al-`Azîz b. Bâz
It is allowed for a fasting person to use an inhaler if needed. Allah says: “He has explained to you in detail what is forbidden to you except under compulsion of necessity.”
Inhalers are not in the form of food and drink. They resembles non-nutritive injections.
[Majmû` al-Fatâwâ (volume 15, page 264)]
Source: Islam Today