Issue taking tablet yourself (6,3)
I believe the answer is:
number one
'yourself' is the definition.
(I've seen this before)
'issue taking tablet' is the wordplay.
'issue' becomes 'number' (synonyms).
'taking' becomes 'on' (eg one taking drugs is 'on' drugs).
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'number'+'on'+'e'='NUMBER ONE'
(Other definitions for number one that I've seen before include "top man?" , "Yours truly" , "Informally the self, numerically speaking" , "Top-of-the-charts hit" , "Informally and numerically, oneself" .)