- History of treatment-resistant OCD, established by a trained psychiatrist with extensive expertise in the OCD field. Treatment-resistance is defined as non-response (less than 25% reduction of the Y-BOCS score) after at least one SRIs trials (clomipramine, fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram, escitalopram) at the maximum tolerable dose for at least 12 weeks.