There has certainly been a tremendous backlash against the "neurotransmitter imbalance" theory of depression and other mood disorders. That's a whole subject unto itself. Perhaps I only have a superficial understanding of this, but from some of the websites, it seems that the theory of pyroluria at least in the context of mood disorders is that it causes neurotransmitter imbalances. I am finding it hard to reconcile how the same people who (perhaps rightly) decry the biochemical hypotheses that have been used to market antidepressants seem to embrace the same hypotheses in the context of pyroluria. Example, this doctor slams the whole notion of serotonin deficiency, very persuasively. http://kellybroganmd.com/depression-serotonin/ Yet elsewhere, in answering questions, she gives her approval of treating for pyroluria.