Limited Efficacy of 3  mA Intensified tDCS of the Right Inferior Frontal Cortex for OCD Treatment: A Randomized, Double‐Blind, Sham‐Controlled Study

OBJECTIVE: Transcranial direct current stimulation (tDCS) has been proposed for treating obsessive-compulsive disorder (OCD) with advantages such as affordability and home-use application. Despite a moderate therapeutic effect, previous findings have been mixed. This registered, randomized, double-blind, sham-controlled trial investigated the efficacy of an intensified tDCS protocol targeting the inferior frontal cortex (IFC), a relevant brain region for inhibitory control for OCD treatment. METHODS: Forty patients with OCD received 20 sessions of 3 mA intensified tDCS or sham tDCS in parallel groups. The active treatment included 20 sessions of 20-min 3 mA stimulation delivered twice per day (in 2 weeks) with 20-min between-session intervals. Intervention efficacy, treatment response, and cognitive functions (response inhibition, cognitive flexibility, and sustained attention) were evaluated before and after the intervention and at 2-week, 1-month, and 3-month follow-ups. RESULTS: Blinding of patients was successful. Both groups experienced decreased OCD symptoms, anxiety, and depression. While the active tDCS group showed a significant reduction in all clinical measures from pre- to post-intervention, no statistically significant between-group differences were found. The active tDCS group showed a mean reduction of 22.38% in OCD symptoms from baseline to endpoint, with 20% (4/20) responding with ≥ 50% symptom reduction, compared to 15.25% and 0% (0/20) in the sham group. Cognitive assessments similarly revealed within-group improvements over time, but no differences between groups. CONCLUSIONS: 3 mA tDCS over the right IFC showed limited efficacy for OCD treatment, likely confounded by placebo effects, suggesting that other targeted regions may be more promising for tDCS intervention. TRIAL REGISTRATION: IRCT20230216057437N1.