Call me up -- that's sickening (6)
I believe the answer is:
emetic
'sickening' is the definition.
(I've seen this before)
'call me up' is the wordplay.
'call' becomes 'cite' (citing is a kind of calling).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'cite'+'me'='citeme'
'citeme' written backwards gives 'EMETIC'.
'that's' acts as a link.
(Other definitions for emetic that I've seen before include "Nauseating" , "A medicine to induce nausea" , "Vomiting inducer" , "Inducing vomiting" , "Cite me as containing sick-making substance" .)