Depression and chronic pain frequently co-occur, amplifying disease burden and complicating treatment. Shared mechanisms span immune, neurotransmitter, and neuroplastic domains. Neuroinflammation, characterized by elevated cytokines such as IL-6 (interleukin-6) and TNF-α (tumor necrosis factor-alpha), drives both mood dysregulation and nociplastic pain through microglial activation and central sensitization. Dysregulation of glutamate and gamma-aminobutyric acid (GABA) signaling contributes to excitatory-inhibitory imbalance, while altered BDNF (brain-derived neurotrophic factor) expression links neuroplasticity with pain amplification. Substance P and monoamine disturbances further integrate affective and somatic symptoms. Neuroimaging reveals overlapping dysfunction in prefrontal, cingulate, and limbic networks, providing a unifying framework for pain-emotion interactions. Psychological and social factors, including maladaptive cognitions, emotion regulation deficits, and reduced social support, exacerbate this bidirectional relationship. Clinically, tricyclic antidepressants and SNRIs (serotonin-norepinephrine reuptake inhibitors) demonstrate superior analgesic efficacy compared with SSRIs, particularly in neuropathic pain, fibromyalgia, and irritable bowel syndrome. Novel agents such as ketamine and esketamine show rapid antidepressant and potential analgesic effects. Neuromodulation strategies (rTMS (repetitive transcranial magnetic stimulation), tDCS (transcranial direct current stimulation)) and psychological interventions (CBT (cognitive behavioral therapy), mindfulness, ACT (acceptance and commitment therapy)) further enhance outcomes. Together, these findings support a precision medicine approach that integrates biological, psychological, and social determinants. Targeting convergent mechanisms may reduce symptom burden, improve treatment responsiveness, and ultimately enhance quality of life in patients with comorbid depression and chronic pain.
