Processed hemp, not changed, causes stress (8)
I believe the answer is:
emphasis
'stress' is the definition.
(I know that stress can be written as emphasis)
'processed hemp not changed' is the wordplay.
'processed' indicates anagramming the letters.
'not changed' becomes 'as is' (I've seen this before).
'hemp' is an anagram of 'emph'.
'emph'+'asis'='EMPHASIS'
'causes' acts as a link.
(Other definitions for emphasis that I've seen before include "Stress, special importance" , "Stress laid on, eg, words" , "Weight" , "Force" , "Stress given to a word" .)