Elevated allostatic load is associated with poorer response to repetitive transcranial magnetic stimulation in treatment-resistant depression

•There is a relationship between allostatic load and major depressive disorder.•It is essential to identify biomarkers that predict antidepressant response.•Increased pre-treatment allostatic load can predict response to repeated transcranial magnetic stimulation. This cohort study investigated whether allostatic load (AL) is associated with treatment response to repetitive transcranial magnetic stimulation (rTMS) in treatment-resistant depression (TRD). Pre-treatment blood samples measured AL across multiple systems. Pre- and post-treatment mood changes were assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS). Associations between AL and treatment outcomes were explored. Higher pre-treatment AL was significantly associated with poorer post-treatment response status but was not significantly associated with smaller reduction in MADRS score after 4 weeks of treatment. Identifying biomarker profiles informed by the AL model could enhance treatment decisions in TRD, reducing risks associated with prolonged, ineffective rTMS trials and emphasizing the need for reliable predictive biomarkers.