The Collaborative International Dictionary of English v.0.48:

Alleviative \Al*le"vi*a*tive\, a.
   Tending to alleviate. -- n. That which alleviates.
   [1913 Webster]

WordNet (r) 3.0 (2006):

alleviative
    adj 1: moderating pain or sorrow by making it easier to bear
           [syn: alleviative, alleviatory, lenitive,
           mitigative, mitigatory, palliative]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "alleviative":
   alleviating, alleviator, analgesic, anesthetic, anodyne, assuager,
   assuasive, balm, balmy, balsamic, benumbing, calmant, calmative,
   cathartic, cleansing, cushion, deadening, demulcent, disburdening,
   disencumbering, dolorifuge, dulling, easing, emollient, lenitive,
   lightening, mitigating, mitigative, mitigator, moderator,
   modulator, mollifier, numbing, pacificator, pacifier, pain-killing,
   palliative, peacemaker, purgative, relieving, remedial,
   restraining hand, salve, sedative, shock absorber, softening,
   soother, soothing, soothing syrup, stabilizer, subduing, temperer,
   tranquilizer, unburdening, wiser head