The causes of mental illness remain obscure in spite of rapid progress in the neurosciences. This is due in part to the fact that contemporary biomedical psychiatry rests on philosophically and scientifically ambiguous ground. In Western medicine paradigms, theories from physics, chemistry, and biology form the basis of an explanatory model of illness, including mental illness. Symptoms are conceptualized as subjective descriptions of effects caused by factors characterized in empirical terms. Conventional biomedicine asserts that all causes of illness, and by extension, mechanisms of action underlying legitimate treatment approaches, rest on biological processes that can be described in the reductionist language of Western science. However, in contemporary Western psychiatry, there is no single adequate explanatory model of the causes of mental illness. What remains are competing psychodynamic, genetic, endocrinologic, and neurobiological models of symptom formation reflecting disparate ideological positions and diverse clinical training backgrounds of mental health professionals. There is no unifying theory in psychiatry because no single explanatory model has been confirmed as more valid than any other. I hypothesize in this article that the synthesis of ideas and clinical approaches from Western biomedicine and non-Western systems of medicine based on understandings of human consciousness, the neurosciences, complexity theory, and quantum field theory, will lead to rapid evolution of conventional Western biomedical psychiatry toward truly integrative mental healthcare. The result will be the emergence of an integrative mental healthcare model that will more adequately address the disparate causes, conditions, and meanings of symptoms combining multimodal approaches from Western biomedicine and non-Western systems of medicine.