This can be a very sensitive issue, especially if he choose to come off of medication on his own accord. Especially if they were making other health issues worse. I'd say to just be very careful. As someone with OCD, I know it can be scary when someone brings up medications because it's one of my intrusive thoughts; that medication will kill me, etc.

Maybe ask him how he is feeling. Ask if he thinks there is anything that would help him manage his OCD, and go from there. Good luck.