The Collaborative International Dictionary of English v.0.48:

allergic \allergic\ adj.
   1. of or pertaining to allergy. allergic reaction
      [WordNet 1.5]

   2. 1 having an allergy or peculiar or excessive susceptibilty
      especially to a specific factor allergic children

   Syn: hypersensitive, hypersensitized, sensitized,
        supersensitive, supersensitized
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

allergic
    adj 1: characterized by or caused by allergy; "an allergic
           reaction"
    2: having an allergy or peculiar or excessive susceptibility
       (especially to a specific factor); "allergic children";
       "hypersensitive to pollen" [syn: allergic,
       hypersensitive, hypersensitized, hypersensitised,
       sensitized, sensitised, supersensitive,
       supersensitized, supersensitised]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "allergic":
   anaphylactic, anemic, apoplectic, arthritic, averse, bilious,
   cancerous, chlorotic, colicky, consumptive, delicate, disaffected,
   disenchanted, disinclined, displeased, dropsical, dyspeptic,
   edematous, empathetic, empathic, encephalitic, epileptic, goosy,
   hostile, hyperesthetic, hyperpathic, hypersensitive, irritable,
   itchy, laryngitic, leprous, luetic, malarial, malignant, measly,
   nephritic, nervous, neuralgic, neuritic, not charmed, overrefined,
   oversensible, oversensitive, overtender, palsied, paralytic,
   passible, phthisic, pleuritic, pneumonic, pocky, podagric, prickly,
   put off, rachitic, refined, responsive, rheumatic, rickety,
   scorbutic, scrofulous, sensitive, skittish, supersensitive,
   sympathetic, tabetic, tabid, tactful, tender, tetchy, thin-skinned,
   ticklish, touchy, tubercular, tuberculous, tumorigenic, tumorous,
   unfriendly