Dear so so sad
I'm really sorry to hear that your son is going through something similar, the important thing is to never give up and try to make sure he doesn't drop out of society (I did for 22 years) as his anxiety and depression will only increase even more. What do you think of Maxima?
Also, what worked for me was this: First I went to a psychiatrist and was put on an SSRI, which made so much difference, then I found psychologist that was a good fit for me. My anxiety and depression was so bad that a psychologist was essentially useless, I simply couldn't fight the level of negativity my mind was throwing at me - the only break I got was when I slept. This all changed with the medication and nutrient therapy.
Sadly the SSRI ceased to be very effective after a while, so I found a nutrient therapy - google the 'Walsh Research Institute' and 'The Australasian College Of Nutritional And Environmental Medicine' I found a GP in Sydney there that uses the Walsh protocol. The people at walsh have a database with over 30,000 patients, with an 80% success rate. It cured my depression, reduced my anxiety (to moderate social from GAD where I could barely leave my bedroom), and greatly reduced my OCD. It literally saved my life. There is a book 'Nutrient Power' by William J. Walsh that explains all of this, I got it at the Book Depository.
I also found fish oil helpful (ignore if your son has a bleeding disorder) - I've read that it helps some people, but not all. I truly hope that all of this helps