Introduction Pharmacotherapy and cognitive behavioural therapy (CBT) are consistently effective as first-line treatments for social anxiety disorders (SADs). Nevertheless, pharmacotherapy is often the first choice in clinical practice. In many countries, the first line of pharmacotherapy involves the administration of a selective serotonin reuptake inhibitor (SSRI). Although a significant proportion of patients with SAD fail to respond to the initial SSRI administration, there is no standard approach to the management of SSRI-resistant SAD. This paper describes the study protocol for a randomised controlled trial to evaluate the clinical effectiveness of CBT as a next-step strategy, concomitant with conventional treatment, for patients with SSRI-resistant SAD.

Methods and analysis This Prospective Randomized Open Blinded End-point study is designed with two parallel groups, with dynamic allocation at the individual level. The interventions for the two groups are conventional treatment, alone, and CBT combined with conventional treatment, for 16 weeks. The primary end-point of SAD severity will be assessed by an independent assessor using the Liebowitz Social Anxiety Scale, and secondary end-points include severity of other social anxieties, depressive severity and functional impairment. All measures will be assessed at weeks 0 (baseline), 8 (halfway point) and 16 (postintervention) and the outcomes will be analysed based on the intent-to-treat. Statistical analyses are planned for the study design stage so that field materials can be appropriately designed.

Ethics and dissemination This study will be conducted at the academic outpatient clinic of Chiba University Hospital. Ethics approval was granted by the Institutional Review Board of Chiba University Hospital. All participants will be required to provide written informed consent. The trial will be implemented and reported in accordance with the recommendations of CONSORT.

Clinical Trial Registration Number UMIN000007552.