Go mad, crackers, teaching (5)
I believe the answer is:
Here is my best explanation:
'teaching' is the definition.
(dogma is a kind of teaching)
'go mad crackers' is the subsidiary indication.
'crackers' indicates an anagram (informal term for mad).
'gomad' anagrammed gives 'dogma'.
(Other definitions for dogma that I've seen before include "Code of belief", "Religious principles", "church teaching", "Authoritative doctrine", "Opinion viewed as truth?", "Doctrine accepted as true without proof", "Non-evidence based opinion", "fixed opinion", "Principles laid down by authority as true" and "Doctrine laid down with authority".)