Clue: Weirdo makes illegal drugs (8)
Answer: CRACKPOT
Explanation: Definition: Weirdo
CRACK + POT are both illegal drugs. 
I may be splitting hairs, but I'd say that the clue should say "illegal drugs make weirdo".
 
Think of the clue as a sum, with "weirdo" = 4, "crack" = 3, and "pot" = 1.
 
We would say that 1 and 3 makes 4, but we wouldn't say that 4 makes 1 and 3.