Been there, done that one though my daughter was never officially diagnosed. Depression runs in my family and she's had her share of issues, especially around her dad and I's divorce and her own weight issues. She was threatening suicide at 8 years old.
First off, I hope he's not just on drugs. He needs to be in therapy as well. Drugs don't solve everything especially if the reason the depression was brought on by a traumatic event or something else specific. If it's strictly chemical then he still needs it to learn how to cope and strategies for handling things when it gets bad.
Some things that worked with my daughter are: making her write out sticky notes saying positive things about herself, letting her know that it's ok to talk about how she feels even the sad feelings, getting her to write in a journal, getting her involved in physical activity on a regular basis, even just playing catch in the backyard or a daily walk (this effects brain chemistry in a positive way and can help lessen the symptoms), quiet time when she gets in trouble and then calmly talking about it after, working on a family project like a giant puzzle or something you both enjoy, and other ways. Everyday near bedtime I would ask "Ok, now tell me something positive about today".
Something that's important to do is always remind him how much you love him and are still proud of him, no matter what. Even when my daughter gets in trouble I tell her "I love you but this is not acceptable." Also ensure he knows he doesn't need to feel ashamed of this diagnosis. It is an illness as surely as any other.
It takes a lot of patience dealing with a child with this illness. What about looking up a support group for yourself? They have a ton of ideas to help and it's good to know you're not alone.
I don't know if any of this was a help or not. Each child is different but I hope things improve for you soon.