The goal of this brief review is to explain the role of monoamine oxidase enzymes in the neurobiology, etiology, and presentation of psychiatric illnesses, primarily major depressive disorder. This article will initially focus on the basic science and function of the monoamine oxidase system and some proposed neuropsychiatric symptoms that may arise if this enzyme system is altered by genetic predisposition. These findings and theories will next be translationally discussed in regard to clinical application pertaining to enzyme inhibition and the treatment of major depressive and other psychiatric disorders.

There are several investigational drugs in development for the treatment of depression. Some of the novel antidepressants in development target monoaminergic neurotransmission in accordance with the “monoamine hypothesis of depression.” However, the current conceptualization of antidepressant actions is that it is the downstream effects on protein synthesis and neuroplasticity that account for therapeutic efficacy, rather than the immediate effects on synaptic monoamine levels. Thus, a number of novel agents in development directly target components of this “neuroplasticity hypothesis of depression,” including hypothetically overactive glutamatergic neurotransmission and dysfunctional hypothalamic–pituitary–adrenal (HPA) axis functioning.

Although not all individuals who work outside of standard daytime hours develop physical and psychiatric issues, there is a substantial portion of shift workers who develop shift work disorder. Shift work disorder is due to a misalignment between an individual's endogenous circadian rhythms and environmental stimuli, and can have potentially serious consequences to an individual's health and quality of life. This article reviews the neurobiological and genetic underpinnings of shift work disorder, and describes how desynchronization of the molecular clock may lead to both physical and psychiatric illnesses. Diagnostic tools and treatment guidelines to address the circadian misalignment, excessive sleepiness, and insomnia experienced by patients with shift work disorder are also discussed.

Long-acting injectable (LAI) antipsychotics can have considerable advantages over oral medications for the management of patients with schizophrenia. Despite the high prevalence of treatment nonadherence with oral pharmacotherapy, LAI antipsychotics are significantly underutilized in this patient population. The availability of newer LAI antipsychotic preparations combined with a resurgent interest in the use of typical antipsychotics has rekindled awareness of the value of LAI medications. This article is intended to provide a visual understanding of the various kinetic profiles of LAI antipsychotics to facilitate initiation and greater use of these agents.