What stops pub relapse?! (5)
I believe the answer is:
rehab
'relapse?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'what stops pub' is the wordplay.
'what' becomes 'eh' (sound used to ask 'what?' or 'pardon?').
'stops' is an insertion indicator (stopping can mean blocking a gap).
'pub' becomes 'rab' (I can't explain this - if you can you should believe this answer much more).
'eh' going inside 'rab' is 'REHAB'.
Can you help me to learn more?
(Other definitions for rehab that I've seen before include "Treatment for alcohol abuse" , "Treatment for dependency" , "Treatment for alcoholism" , "A herb (anag.)" , "Alcohol clinic" .)