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]

WordNet (r) 3.0 (2006):

contraindicate
    v 1: make a treatment inadvisable [ant: indicate, suggest]