From The Collaborative International Dictionary of English v.0.48 :
Contraindicate \Con"tra*in*"di*cate\, v. t. [imp. & p. p.
Contraindicated; p. pr. & vb. n. Contraindicating.]
(Med.)
To indicate, as by a symptom, some method of treatment
contrary to that which the general tenor of the case would
seem to require; especially, to indicate that a particular
method of treatment should not be used; as, penicilin is
contraindicated in patients who have shown hypersensitivity.
[1913 Webster +PJC]
Contraindicating symptoms must be observed. --Harvey.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
contraindicate
v 1: make a treatment inadvisable [ant: indicate, suggest]