More vacuous politician caught in drug row (7)
I believe the answer is:
emptier
'more vacuous' is the definition.
('empty' can be a synonym of 'vacuous')
'politician caught in drug row' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'caught in' indicates putting letters inside.
'drug' becomes 'e' (E is another name for ecstasy).
'row' becomes 'tier' (a tier is a row of things).
'e'+'tier'='etier'
'mp' inserted inside 'etier' is 'EMPTIER'.
(Other definitions for emptier that I've seen before include "more in need of food" , "Being more hungry" , "Containing less" , "I'm Peter (anag)" , "More vacuous" .)