Hi, I'd like to help you with your question.
It sounds like your son first needs to see his doctor about his medication. He may be on too much or need a change in medicine. Was he like this before? If not, then a medication check should help.
Part of his depression and lack of motivation may be the fact that he does not have any responsibilities. Your son should have more responsibilities at his age than he does right now. If he is living with you, he should be contributing to the household budget. If he cannot afford it, he needs to at least contribute to the household chores. Hold him to this. If he won't contribute, then talk about having him move out. That way, if he choses to sleep all day, it's on him. And if he wants to play games most of the day, he'll be the one responsible for the consequences. It is the only way he will begin to understand responsibility and become motivated to be in charge of his own life.
Helping your son with his gaming addiction is going to require his cooperation. If you feel he is ready to address this problem, he can see a counselor. He can find one through his doctor or if he attends church, his pastor can help. He can also search on line at http://therapists.psychologytoday.com/rms/.
First, to address his addiction, he must be willing to admit to it. Owning up to having a problem is important. As long as he is denying it, he will not willing to get help. Once he is able to realize he has a problem, he can go online for help. Here is the link for online gamers anonymous- http://www.olganon.org/. They can provide guidance and help him understand how to address his addiction. He also needs support. Family, friends and others who have experienced gaming addiction, or other addictions can help him. He needs someone to turn to if he feels the need to play again. This is where a sponsor or other support person can help.
Here are some books that will help as well:
Cyber Junkie: Escape the Gaming and Internet Trap by Kevin J. Roberts
Unplugged: My Journey into the Dark World of Video Game Addiction by Ryan G. Van Cleave and Mark Griffiths
When Gaming becomes an Obsession: Help for Parents and their Children to Treat Online Gaming Addiction by XXXXX XXXXX
These are available on Amazon.com (some are Kindle editions) or check with your local library.
I hope this has helped you,