Hallucinogen produced from stale dung (5,4)
I believe the answer is:
Here is my best explanation:
'hallucinogen' is the definition.
(angel dust is a kind of hallucinogen)
'from stale dung' is the subsidiary indication.
'from' indicates an anagram (from the letters).
'staledung' anagrammed gives 'angeldust'.
'produced' is the link.
(Other definitions for angel dust that I've seen before include "Hallucinogen - stale dung (anag)" and "Drug".)