To be honest I think Caregiver222 and JGF25 said it very well. Has he tried therapy to help deal/cope with his OCD? I am not a doctor so correct me if i am wrong but I believe that most psychiatrist drugs such as anti depressants have not been tested or approved for children under the age of 18 and i would defiantly be on caution when using it someone under 18 because the side effects can be very dangerous including suicidal thinking and plans, so needs to be carefully monitored by a psychiatrist. Plus i would talk to his doctor about CBT a form of therapy which might be very helpful.
Good luck
I guess the better question is why is he refusing? He has obviously been diagnosed with OCD. He was doing something that landed him at the doctor's office to get a formal diagnosis and the doctor thought it warranted medication. This is a very tough question to answer when I don't know the facts surrounding his OCD. Perhaps it is a very mild form and he thinks medication is not necessary??? Has he tried the medication? There are side affects with most of these medications and perhaps those are bothering him? I'm just guessing here.....
His refusal is not entirely without basis. I would speak with him and discuss this, preferably in the presence of his physician/psychiatrist. At the same time you should ask and research alternate treatments, including strict diets. He has a right to refuse medications that should be respected.