Trouble with endless Viagra, get off tablet (8)
I believe the answer is:
aggrieve
'trouble' is the definition.
(I've seen this before)
'endless viagra get off tablet' is the wordplay.
'endless' says to take the centre.
'get' is a charade indicator (letters next to each other).
'off tablet' becomes 'grieve' (I can't explain this - if you can you should give a lot more credence to this answer).
The middle of 'viagra' is 'ag'.
'ag'+'grieve'='AGGRIEVE'
'with' acts as a link.
(Other definitions for aggrieve that I've seen before include "Distress, injure" , "Cause annoyance to" , "Cause to feel sorrow" , "Do an injustice to" , "Break the heart" .)