Slimy stuff ends in giving you anaphylactic shock (4)
I believe the answer is:
guck
'slimy stuff' is the definition.
(I've seen this in another clue)
'ends in giving you anaphylactic shock' is the wordplay.
'ends in' says to take the final letters.
The last letters of 'giving you anaphylactic shock' are 'GUCK'.
(Other definitions for guck that I've seen before include "Sludge" , "Gooey muck" , "Slimy muck (sl.)" .)