Mentally ill - needs a change of routine before cure starts (8)
I believe the answer is:
neurotic
'mentally ill' is the definition.
(thesaurus)
'a change of routine before cure starts' is the wordplay.
'a change of' indicates an anagram (the letter order is changed).
'before' is a charade indicator (letters next to each other).
'starts' indicates taking the first letters.
The initial letter of 'cure' is 'c'.
'routine' anagrammed gives 'neuroti'.
'neuroti'+'c'='NEUROTIC'
'needs' acts as a link.
(Other definitions for neurotic that I've seen before include "Subject to excessive anxieties and abnormal behaviour" , "Very nervy" , "Subject to excessive anxiety and behaviour" , "Paranoid" , "Abnormally obsessive" .)