Augmentation treatment has been the subject of several studies in treatment-resistant obsessive compulsive disorder (OCD). We hypothesized that medications with a dual action on the melatoninergic and serotoninergic systems may be of use in treatment-resistant OCD.

In this open label study we investigated the efficacy and safety of agomelatine augmentation in treatmentresistant OCD.

Twelve patients, aged 18–50, fulfilling OCD criteria, with no response to a 16-week or longer treatment with a selective serotonine reuptake inhibitor (SSRI) at the indicated dose, were assigned to receive agomelatine augmentation. Subjects were assessed with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), and were screened for treatmentemergent side effects at baseline, week 8 and week 12 of treatment.

The overall Y-BOCS score fell during the duration of the study (all comparisons among baseline, 8^th week and 16^th week were statistically significant, p<0.01). On the obsession Y-BOCS scale a drop was noted, which led to statistical significance at the 16^th week of the study (p<0.05). Regarding the compulsion Y-BOCS scale a drop was also noted, particularly from baseline to the 8^th week of the study (p<0.01). Dizziness (16.6%) and headache (8.4%) were the most often reported side effects of treatment.

Agomelatine could be efficacious and well tolerated as an augmenting agent in refractory to treatment OCD. Further controlled studies are warranted to explore the efficacy of agomelatine, as well as the potential role of circadian rhythm modulation both in the pathophysiology and treatment of OCD.