All drugs are used for treatment of OCD except:
Carbamazepine
Lithium
Fluoxetine
Diazepam
Again, we have to choose between Carbamazepine and diazepam. Now, diazepam is a benzodiazepine and can improve anxiety temporarily however it doesn't act at core symptoms of OCD. Whereas, Carbamazepine, though has minimal evidence, but it has been found to act on core symptoms of OCD.
Neurotic, Stress Related and Somatoform Disorders