Methods and systems are described for determining, in a patient that suffers from a mood disorder (e.g., depression), a propensity of the patient to manifest reduced symptoms or levels of indicators of the mood disorder in response to a psychiatric treatment. This can involve determining levels of a marker (e.g., a metabolite) indicative of a brain bioenergetic state of the patient that is predictive of whether the patient will response favorably to an antidepression treatment. Such bioenergetic state markers, tending to normalize in response to antidepression therapy, can include, e.g., a pH, a magnesium level, and a phosphorus level. Brain levels of such markers can be determined by, e.g., 31P MRS.