When I was looking into it I found that it was just as if not more effective than SSRI's If you can afford it as its not subsidized by the government. This site had the most in depth info on it:
5HTP - The Natural Alternative to Prozac: Chapter 1
Also the Professor Irving Kirsch holds a chair in psychology at the University of Hull. His research interest has long been the placebo effect and last year he and colleagues published a paper which exploded on to the public arena when they used the Freedom of Information Act to access data that hadn't seen the light of day before from pharmaceutical company trials of antidepressants.
Irving Kirsch: "In fact 40% of the studies that are sponsored by the drug companies evaluating antidepressant medication, 40% of them are not published. If you look at the published studies you get a very pleasing picture, it makes a nice story. Most of the published trials show that antidepressants are more effective than placebos. We now know that if you look at the unpublished trials sponsored by the same pharmaceutical companies you get a very different story. In those trials very few of them show significant differences between drug and placebo".
If you like to read the whole transcript or listen to the audio heres the link:
All In The Mind - 23 May 2009 - Antidepressants, placebo and medicalising mood
In my opinion antidepressants for OCD are a half assed alternative to 5ht2A agonist like psilocybin, LSD, mescaline etc. which have been shown to have drastic effects on OCD symptoms if not alleviating them all together. From my understanding their benificial effect is acheived in much the same way as the antidepressants but is far more effective due to their higher affinity for the 5ht2A receptor, and abilility to be safely consumed in potent doses. I'm not 100% sure if I'm right but I think this beneficial effect is due to their indirect down regulation of the 5ht2A receptor. In other words once the body recieves a substance that acts as a potent 5ht2A receptor agonist the body picks up on it's higher receptivity, and overtime if it continues the body will naturally down regulate it. People with ocd are thought of having an over active number of 5ht2A receptors in the brain so while the consumed 5ht2A agonist is in the process of indirectly inducing the body into natural down regulation at these receptors the body must somehow detect that these receptors regular day to day activity is also too high as previously explained is the case with OCD, and return its receptivity to whats considered a normal level here by elevating ocd symptoms. Again I'm not 100% sure but I also believe the action the body uses to naturally return this receptor to whats considered normal operation is still not yet fully understood but the way potent 5ht2A agonists alert the body to this receptors irregular day to day activity is the key to their drastic effects on ocd as skipping this step by taking a direct 5ht2A antagonist such as a atypical anti psychotics although benifical in low doses due their inhibitory effect on the dopamine receptors has been shown to have little effect due to their 5ht2A antagonism, and at high doses can actually dramatically worsen ocd symtoms from this antagonism.
Hope this helps