A 42-year-old patient has been diagnosed with major depressive disorder and has undergone trials of two different SSRIs and one SNRI at therapeutic doses for appropriate durations, with minimal improvement in symptoms. The psychiatrist now suspects treatment-resistant depression. Which is the most appropriate next step in management?

Choice A reason: Exceeding antidepressant doses risks serotonin syndrome or toxicity, as SSRIs/SNRIs already maximize serotonin/norepinephrine reuptake inhibition. Treatment-resistant depression involves complex monoamine and glutamate imbalances in the prefrontal cortex and hippocampus. Overdosing fails to address these, potentially worsening side effects like agitation, without improving synaptic plasticity or mood regulation. Choice B reason: Discontinuing antidepressants for psychotherapy alone ignores neurobiological deficits in treatment-resistant depression, including reduced prefrontal cortex serotonin and hippocampal neurogenesis. Psychotherapy engages cognitive circuits but lacks direct impact on monoamine or glutamate systems. Abrupt cessation risks withdrawal and symptom worsening, making this inadequate as a standalone next step. Choice C reason: Aripiprazole, an atypical antipsychotic, modulates dopamine D2 and serotonin 5-HT1A/5-HT2A receptors, enhancing prefrontal cortex and hippocampal function in treatment-resistant depression. Augmentation addresses serotonin and glutamate imbalances, promoting synaptic plasticity and mood stabilization. Clinical evidence supports its efficacy when SSRIs/SNRIs fail, making it a scientifically grounded next step. Choice D reason: ECT is effective for severe depression but is typically reserved for life-threatening cases due to cognitive side effects and invasiveness. It induces seizures, altering glutamate and GABA in the cortex, but treatment-resistant depression first warrants less invasive augmentation. ECT’s neuroplasticity benefits are significant but not the immediate next step here.