A meta-analysis included 41 randomized controlled trials that compared CBT with placebo.1 In 34 of these studies, the intervention was delivered on an individual basis, whereas in the remaining 7 studies CBT was delivered to groups.1 There was a mean of 11 CBT sessions across the studies. 1 Overall, there was an almost threefold higher response rate with CBT vs placebo.1

Reference:
1. Carpenter JK, Andrews LA, Witcraft SM, et al. Cognitive behavioral therapy for anxiety and related disorders: a meta-analysis of randomized placebo-controlled trials. Depress Anxiety 2018; 35 (6): 502–514.