Placebo effects are a major factor in allergy trials - a significant amount of the efficacy in all allergy products appears to be caused by the expectation that they will work.

In the most recent manifestation of the problem, the results of ImmuLogic Pharmaceutical Corp.'s Phase III cat room challenge trial of its Allervax Cat allergy product may have been hurt by the high expectations of patients following the good results of the company's Phase II study.