Dispenser that relieves congestion popular in some monarchal eras (7)
I believe the answer is:
inhaler
'dispenser that relieves congestion' is the definition.
'inhaler' can be an answer for 'dispenser' (inhaler is a kind of dispenser). I am not sure about the rest of the definition.
'popular in some monarchal eras' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'in some monarchal eras' becomes 'haler' (I can't justify this - if you can you should believe this answer much more).
'in'+'haler'='INHALER'
Can you help me to learn more?
(Other definitions for inhaler that I've seen before include "Asthmatic's device" , "Eg, asthma reliever" , "Respiratory aid" , "Asthmatic's aid" , "gas mask" .)