### Clue: In vain, try to sell a drug after being affected by anaesthetic (4,1,4,5)
### Answer: FLOG A DEAD HORSE 
 ### Explanation: Definition: In vain
 FLOG(try to sell, perhaps even, a lame or dead horse) + A + [ HORSE(slang for the drug heroin) **placed below**(after, in a down clue) DEAD(to the world after being given a general anaesthetic) ].