Reason to use an inhaler (6)
I believe the answer is:
asthma
'reason to use an inhaler' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asthma that I've seen before include "Mat has a respiratory disorder" , "Cause of breathing difficulty" , "which leaves one breathless" , "Respiratory problem" , "Lung condition" .)