Depression involves complex interactions between neurotransmitter systems (serotonin, norepinephrine, dopamine, glutamate), neural circuits in the prefrontal cortex and limbic system, and inflammatory and stress-response pathways. Standard antidepressants primarily target monoamine neurotransmitters, which helps many patients but does not fully address every biological driver.
According to the NIMH on depression, roughly one in three adults with major depressive disorder does not achieve remission with conventional medication alone. When the underlying circuitry is dysregulated beyond what monoamine-based medications can correct, symptoms persist despite adequate trials.
TRD is also influenced by factors like medication metabolism (pharmacogenomic differences), co-occurring medical or psychiatric conditions, chronic stress, and unresolved trauma. For many patients, a detailed specialist psychiatric consultation reveals missed contributors that change the treatment plan entirely.
