Repeat my words over a kind of medicine (6)
I believe the answer is:
emetic
'a kind of medicine' is the definition.
(medicine which causes vomiting)
I don't understand how the remainder of the clue works.
(Other definitions for emetic that I've seen before include "It makes one sick" , "making you throw up" , "inducing sickness" , "It sickens one" , "Medicine taken to make one vomit" .)