Can dogs treat depression?

Introduction:

This project I have been working on for a long time is based on a simple question: can dogs help treat or even be a cure for mental illness such as depression or anxiety. These are illnesses which are completely mental and emotional which means they can be treated with common medicine like a virus or bacteria. These illnesses are caused by the body of the person after a traumatic experience which makes them harder to treat because you can't make a person forget and you can't force a person to not be sad, so you can only help a person to try to move on and somewhat ignore the experience or overcome it. Dogs are there for that, to try to make you overcome by giving you company and support and that's why I believe that their treatment can be a replacement for drugs or at least lower their dose in a person's treatment.