Son charges back with ecstasy in short supply (6)
I believe the answer is:
sparse
'in short supply' is the definition.
(sparse can mean meagre or minimal)
'son charges back with ecstasy' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'charges' becomes 'raps' (as in taking the rap).
'back' is a reversal indicator.
'with' means one lot of letters go next to another.
'ecstasy' becomes 'E' (informal term for the drug).
's'+'raps'='sraps'
'sraps' reversed gives 'spars'.
'spars'+'e'='SPARSE'
(Other definitions for sparse that I've seen before include "In short supply" , "not packed together" , "Far from lavish" , "Meagre, thin on the ground" , "Scarce like thinning hair" .)