Tried St. John's wort. Not much of a difference. Took it too long, it made me feel aggressive towards myself. Do not recommend.
Then there is Inositol. Great stuff. It helps with a lot of things, women's issues, immunity,.... you name it, but for ocd you need to take a lot higher dosages daily, and by a lot I mean A LOOOT higher, 18g a day. To compare: for depression or pcos or boosting your immune system anything from 400mg to 2 g helps. It also helps animals. It tastes sweet, like sugar, but less sweet. It is easy to dissolve the powder in juice, tea, water,... but with dosages like 18 g, the side effects were just to unpleasant for me: bloating, Gass, going to the toilet way more often (No 2),... I felt more relaxed but not so much better that it would be worth for me to tolerate the side effects.
I would definitely recommend inositol for all other problems, just with ocd I guess it's up to every person if they want to try it and see how it goes for them. It can't hurt, it does help with a lot of things (if you take it +vitamin C in winter) you will never catch a cold or a virus. Even if you do start coming down with sth, it is a lot milder and goes away in a day or two and not in a week or two.
Vitamin B12, Magnesium, Omega 3, vit D3, Zinc,... all affect our mental health, but they won't cure ocd. The lack will worsen it. It is helpful to have them leveled. But the ocd won't get scared.
Like Matthew said, medicine does help. If one doesn't, there are others. The side effects can be hard to deal with sometimes. Then again, one needs to decide if the benefits outweigh the side effects.
Mindfulness helps. Just like D3, B12,... It won't cure it, BUT DEFINITELY makes coping easier.
Hope I help a bit.
Good luck.