Dismiss special diets containing American drug (3,5)
I believe the answer is:
set aside
'dismiss' is the definition.
(thesaurus)
'special diets containing american drug' is the wordplay.
'special' indicates an anagram.
'containing' indicates putting letters inside.
'american' becomes 'as' (I can't explain this - if you can you should believe this answer much more).
'drug' becomes 'e' (e is another name for ecstasy).
'diets' anagrammed gives 'setid'.
'setid' enclosing 'as' is 'setasid'.
'setasid'+'e'='SET-ASIDE'
Can you help me to learn more?
(Other definitions for set aside that I've seen before include "Discount" , "Reserve(d) in advance" , "Reserve or put away" , "Policy for leaving land alone" , "kept for later" .)