Alcoholic has fling with Mary Jane (7)
I believe the answer is:
tosspot
'alcoholic' is the definition.
(thesaurus)
'fling with mary jane' is the wordplay.
'fling' becomes 'toss' (synonyms).
'with' means one lot of letters go next to another.
'mary jane' becomes 'pot' (synonyms).
'toss'+'pot'='TOSSPOT'
'has' is the link.
(Other definitions for tosspot that I've seen before include "One drinker" , "Habitual drinker" , "One drunkard" , "Drunk (informal)" , "supper, habitually" .)