Synonyms for Frustrating (same or very similar meaning)
WordNet sense 1 (preventing realization or attainment of a desire):
frustrative, thwartingWordNet sense 2 (tending to prevent or hinder):
preventative, preventiveWordNet sense 3 (depriving of confidence or hope or enthusiasm and hence often deterring action):
discouragingFrom the ODE community, based on WordNetadd/edit