Patterns of response during placebo treatment of panic disorder.

Data from the cross-national study of panic disorder are used for an analysis of response patterns. The main purpose of the study is a search for specific placebo patterns and a discussion of possible differences in patterns from patients treated with alprazolam, imipramine, and placebo. Four outcome measures were registered at baseline and weekly during the treatment period: the number of panic attacks, Physician's Global Evaluation of treatment effect, the Overall Phobia Score and the level on the Hamilton Rating Scale for Anxiety. Response patterns from the 3 treatment groups are described and compared, and subsequently categorized with regard to completeness and persistency. No specific placebo pattern is recognized. Some differences are found, however, as many placebo patients demonstrate an early and temporary remission. The variations in response patterns do not compromise the blindness of the study, and their predictive validity is low.