Effect of Daylight Duration on Outcomes of Repetitive Transcranial Magnetic Stimulation in Treatment-Resistant Depression.

Background: To examine the possible impact of daylight duration on the efficacy of repetitive transcranial magnetic stimulation (rTMS) in patients with treatment-resistant depression (TRD). Methods: A retrospective cohort study of 151 patients with TRD undergoing rTMS was conducted. The patient data were collected over multiple years from August 2018 to August 2025. Depression severity was assessed using the Patient Health Questionnaire-9 (PHQ-9) and Hamilton Depression Rating Scale (HDRS) before and after treatment. Patients were categorized into 3 groups: responders, remitters, and nonresponders. Responders were defined by a decrease in PHQ-9 or HDRS score by 50% or more. Remitters were defined by achieving a PHQ-9 score <5 or HDRS score <7. Nonresponders were defined by a change in these scores <50%. Average daylight duration for each individual patient was calculated throughout treatment and compared between groups. Results: The median average duration of daylight in the responder group (n=99) was 704 minutes. The median average duration of daylight in the remitter group (n=62) was 701 minutes, whereas the median average duration of daylight in nonresponders (n=52) was 718 minutes. The Mann-Whitney U test showed no statistical difference in the average daylight duration between the responder and nonresponder groups. Similarly, there was no statistical difference in the average daylight duration between the remitter and nonresponder groups. Conclusion: Based on these findings, daylight duration does not seem to affect rTMS outcomes (response or remission) in patients with TRD. This is reassuring, and if confirmed by future studies, it would mean that rTMS can be delivered at any time of the year without affecting efficacy. Prim Care Companion CNS Disord 2026;28(1):25m04079. Author affiliations are listed at the end of this article.