The Collaborative International Dictionary of English v.0.48:

Stressful \Stress"ful\, a.
   Having much stress. --Rush.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stressful
    adj 1: extremely irritating to the nerves; "nerve-racking
           noise"; "the stressful days before a war"; "a trying day
           at the office" [syn: nerve-racking, nerve-wracking,
           stressful, trying]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "stressful":
   adverse, antagonistic, conflicting, contrary, counter,
   counteractive, detrimental, difficult, draining, exhausting,
   fatiguesome, fatiguing, grueling, hard, harmful, hostile,
   in opposition, inimical, killing, miserable, not easy, opposed,
   opposing, opposite, punishing, rigorous, sinister, straining,
   tiresome, tiring, toilsome, troublesome, troublous, trying,
   unfavorable, untoward, weariful, wearing, wearisome, wearying,
   wretched