Drug provided by popular mainly healthy worker (8)
I believe the answer is:
inhalant
'drug' is the definition.
(thesaurus)
'popular mainly healthy worker' is the wordplay.
'popular' becomes 'in'.
'mainly' means to remove the last letter.
'healthy' becomes 'hale' ('hale' can be similar in meaning to 'healthy').
'worker' becomes 'ant' (worker is a type of ant).
'hale' with its last letter taken away is 'hal'.
'in'+'hal'+'ant'='INHALANT'
'provided by' is the link.
(Other definitions for inhalant that I've seen before include "Medical preparation to be breathed in" , "Medicine for breathing" , "Medicine to breathe" , "Medicinal vapour" , "Vaporised medicine" .)