I can only offer my own evidence, which will be considered anecdotal but I feel that it's worth mentioning: I'm in no way a 'pothead', never liked Phish, played varsity sports. But I had terrible OCD throughout high school and into college. Not "I'm so random I have OCD because I like a clean room" attention seeking OCD. I'm talking full blown, multiple psychiatrists, tried every medication under the sun OCD. Everything was related to numbers for me, and I was never living in the moment because I was constantly doing math in my head to determine: how many steps at a time I should go up/down, if the billboard I just passed was a "good number" or "bad number". Every conversation I had got mentally turned into alphanumeric so I could analyze whether I could trust the person or not (I really trusted sentences that were divisible by 3). It was very consuming of my mental energy. I tried marijuana in college and almost instantly I was able to take a step back and realize that what I was doing was ridiculous and had no bearing on real life. It allowed me to have a rich social life and actually vastly improved my grades since I could fully concentrate in class. In retrospect, it was the first time in my life I felt 'free' because I wasn't constantly mentally preoccupied. I don't live in a Mmj state anymore, and don't have access to it like I used to. My OCD is still pretty much gone due to my usage several years ago in school. I wish I did live in a Mmj state because I sometimes feel it creeping back but I still have the perspective it have me back then to take control of my life and live in the moment.

Tl; dr: trying marijuana in college cured my severe OCD