St. John's Wort is the only clinically demonstrated herbal aid for OCD, and works as good as any antiobsessional drugs.
You can not use St. John's Wort with other anti-depressants or OCD medicines.
Some may suggest marijuana, but Marijuana (or "pot") is not a good treatment for OCD. It may provide some short term relief, but it ultimately causes symptoms to later worsen. For some people, OCD symptoms were actually trigged by using marijuana. Marijuana can also interfere with OCD medications, prevent new learning in therapy, and make comorbid Depression more severe.