My 30 years of depression ended years ago, the day I took the proper dose (for me) of dessicated (non synthetic) thyroid medication. To cure chronic depression, the first step is to determine if you are hypo-thyroid. From my experience, forget the usual blood test and read the book on hypothyroidism by Dr Broda Barnes, md, phd (deceased) -- after years of research, he found that basal temperature (underarm temp. first thing in a.m.) is best indicator of low thyroid---if below 97.8 f.
If you have low basal temp., search on web Dr Broda Barnes, and choose an M.D. who follows his protocol---an association exists of such physicians. If you follow this advice, it could change your life forever.