Drug to be taken after meals — bother! (5)
I believe the answer is:
tease
'bother' is the definition.
(I know that tease is a more specific form of the action bedevil)
'drug to be taken after meals' is the wordplay.
'drug' becomes 'e' (E is another name for ecstasy).
'to be taken after' means one lot of letters go next to another.
'meals' becomes 'teas' (tea is a kind of meal).
'e' after 'teas' is 'TEASE'.
(Other definitions for tease that I've seen before include "Taunt or bait" , "Playfully make fun of" , "Make playful fun of (someone)" , "Josh" , "Rib, annoy" .)