The Collaborative International Dictionary of English v.0.48:

Counterirritant \Coun"ter*ir`ri*tant\ (-?r"r?-tant), n.,
Counterirritation \Coun"ter*ir`ri*ta"tion\, n.
   See Counter irritant, etc., under Counter, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

counterirritant
    n 1: a medicine applied locally to produce superficial
         inflammation in order to reduce deeper inflammation

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "counterirritant":
   adjuvant, antacid, antidote, buffer, carminative, counteractant,
   counteractive, counteragent, emmenagogue, expectorant, hormone,
   maturative, neutralizer, nullifier, offset, preventative,
   preventive, prophylactic, remedy, vasodilator, vitamin