Microbiome of Depression & Treatment Response to Citalopram

Inclusion Criteria: * Outpatients or inpatients with nonpsychotic major depressive disorder (MDD) or Bipolar I or II Disorder. * A score of \>16 on the QIDS * Outpatients or inpatients for whom antidepressant treatment is deemed appropriate by the treating clinician * Subjects who are between 18-55 years of age Exclusion Criteria: * Contraindications to citalopram treatment * Axis I or II disorder other than depression that is the primary reason for seeking treatment intervention and/or psychiatric care * Subjects diagnosed with Borderline Personality Disorder (BPD) as their primary diagnosis. * For healthy controls, a first degree relative who has been diagnosed with an Axis I disorder * Patients with schizophrenia, schizoaffective disorder, or bipolar I disorder * Antidepressant treatment within 4 days of study (1 week if fluoxetine). Subjects currently on antidepressant medication with subtherapeutic results in terms of depression management after providing informed consent, will undergo a medication taper and discontinuation prior to initiation of citalopram treatment. The subject must be off of previous antidepressants for at least 4 days week prior to starting citalopram (1 week if fluoxetine). The subject will be closely monitored by the research study psychiatrist (with or without additional monitoring from primary clinical psychiatric providers). The medication taper is left up to the research study psychiatrist in consultation with patient's primary care or psych…