It's a laugh breaking up drug transport system (7)
I believe the answer is:
haulage
'transport system' is the definition.
'haulage' can be an answer for 'transport' (I've seen this before). I'm not sure about the 'system' bit.
'it's a laugh breaking up drug' is the wordplay.
'breaking' indicates anagramming the letters.
'up drug' becomes 'e' (E is another name for ecstasy. I am not sure about the 'up' bit.).
'a'+'laugh'='alaugh'
'alaugh' with letters rearranged gives 'haulag'.
'haulag'+'e'='HAULAGE'
Can you help me to learn more?
(Other definitions for haulage that I've seen before include "Road transport" , "Commercial transport of goods" , "Commercial transportation of goods" , "Transportation of heavy goods" , "Transport business" .)