Companion following endless amphetamine talk (6)
I believe the answer is:
speech
'talk' is the definition.
(I've seen this before)
'companion following endless amphetamine' is the wordplay.
'companion' becomes 'ch' (I've seen this in other clues).
'following' says to put letters next to each other.
'endless' means to remove the last letter.
'amphetamine' becomes 'speed' (speed is a kind of amphetamine).
'speed' with its final letter removed is 'spee'.
'ch' after 'spee' is 'SPEECH'.
(Other definitions for speech that I've seen before include "Oration, address" , "Formal discourse to an audience" , "Harangue" , "Verbal communication" , "Vocal communication" .)