Matt123, I am praying for your friend!
Depression is an attack on the mind. It occurs when you feel a lack of hope. Doctors say it is anger turned inward. It happens when you feel anger at a boss or loved one and you feel you can't express it for fear of the loss of love or the loss of a job. Satan will use this as an opportunity to attack your mind. Jesus defeated Satan at the cross and took away his tools of evil so he tries to attack your mind by putting evil thoughts in your mind. You need to bind the Spirit of Heaviness and all evil spirits out of your mind. Put on the full Armor of God and pray a hedge of protection around yourself.