Are all mental problems caused by toxicity and iodine deficiency?

I saw somewhere that the majority of Depression have no physical basis (except excessive stress) and can be corrected with therapy and a change in your way of dealing with things in your life

I always had some doubts about that, how come a great amount of persons taking antidepressants and doing therapy can't ever successfully wean off antidepressants or relapse in more then 50% of the time even when the stressors are out of their lives

My guess is that depression/anxiety always have a physical cause, that was probably initiate by stress, which has to be fixed in order to be totally cured of depression

your thoughts?