Jacob-
I agree with Steve and Moviefan. In alot of cases, marijuana and illegal drugs can increase the symptoms of anxiety or OCD. One time before I smoked, I had read a story about a gentleman that smoked marijuana and then went into respitory distress and died. Now while I was stoned, I started thinking about that and it sent me into an anxiety attack.
The brain has so many chemicals in it, and neurologists are still trying to figure out what all of them do. Putting more chemicals into your brain, especially ones that do not naturally occur there, can be a recipe for severe anxiety symptoms.
I know for alot of us it's very tempting to use alcohol or drugs, becuase were willing to try anything to get the thoughts to stop, but there are always better ways to deal with OCD aside from turning to drugs and alcohol.