Asthmatic is healthier with it for starters! (7)
I believe the answer is:
inhaler
'it for starters' is the definition.
The definition suggests a singular noun which matches the answer.
'asthmatic is healthier' is the wordplay.
'asthmatic' becomes 'in' (I am not sure about this - if you are sure you should believe this answer much more).
'is healthier' becomes 'haler' ('hale' can be similar in meaning to 'healthy').
'in'+'haler'='INHALER'
'with' is the link.
Can you help me to learn more?
(Other definitions for inhaler that I've seen before include "way of taking drugs" , "Drug dispenser" , "Asthmatic's aid" , "Device for breathing in medication" , "Asthmatic's device" .)