Inclusion Criteria:  diagnosis by a psychiatrist of current OCD according to the DSM 5 patients in therapy with a stable SSRI for at least three weeks prior written informed consent.  Exclusion Criteria:  Substance dependence IQ <70 comorbid psychiatric disorders female pregnant or breast-feeding or intend to become pregnant during the period of the study concomitant treatments (rTMS, CBT, other glutamate-modulating drugs)