“My adult son has a severe obsessive-compulsive neurosis. He's always depressed, finding no purpose in life. He dropped out of school, holed up at home. He feels worse every day. He was treated at the clinic, but treatment with psychotropic drugs did not work. I can't find out from anyone, where the son could be treated with natural methods.”
I think, that the best treatment method for your son is psychotherapy. It is widely used by neurosis treatment centers, some clinics and private psychotherapists, who often support psychotherapy with elements of music therapy, dancing etc.. The information you need about the addresses of the centers or clinics should be obtained from the nearest Mental Health Clinic (even in this one, where your son was treated) or at the district clinic.