Caught old king with Ecstasy and another drug (4)
I believe the answer is:
coke
'drug' is the definition.
(coke is a kind of drug)
'caught old king with ecstasy' is the wordplay.
'caught' becomes 'c' (cricket abbreviation**).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'king' becomes 'k'.
'with' means one lot of letters go next to another.
'ecstasy' becomes 'e' (informal term for the drug).
'c'+'o'+'k'+'e'='COKE'
'and another' is the link.
(Other definitions for coke that I've seen before include "something for heating" , "Fuel derived from coal" , "Fuel for heating" , "Carbon fuel" , "Fuel made from coal" .)