For anxiety, remedies include aconite, ignatia, and gelsemium,and there are many others. For depression, there are such remedies as arsenicum album, aurum metallicum and calcarea carbonica.
Your bodies chemistry and nutrition can actually cause disorders in mental conditions. Lack of sleep can also make you behave abstractly. Make sure your diet and nutrition are up to par as well as your exercise. Serotonin levels increase when you pay attention to these aspects of your life. Serotonin increases your feelings of happiness which helps your disorder.
St. John's Wart has been proven to help medium grade depression. For any other mental illness, it is best to seek professional medical advice and prescription medication. Do not self treat mental disorders.
Yes, there are homeopathic remedies available for a mental disorder. They treat with certain pills dipped with certain liquids which sharpen your mental ability and thereby reducing mental disorder.