Is there a natural and (preferably) vegan way to treat mental health illnesses (depression etc)?

Depression treatment: Alternative treatments for depression include exercise, eating a healthy diet, therapy, herbal supplements ( i.e. 5 htp, same and st john's wort), journaling and light therapy. Vitamins can also be helpful such as a b complex, vitamin d and omega 3.

Yes: I agree with dr. Howell's ideas, and want to add classical homeopathy as a safe, natural, and effective option when used prudently. Mental health conditions are usually complex and long-standing; for effective treatment you need an experienced classical homeopath to take your case & prescribe the one out of 3000-4000 possible remedies best suited to you. Your progress needs ongoing review also.