Background: Theta burst stimulation (TBS) is a novel and faster modality of transcranial magnetic stimulation, which is showing promise as a treatment-resistant depression (TRD) treatment. Though TBS can be applied unilaterally or bilaterally, few studies have compared the effectiveness of both approaches in a naturalistic clinical sample. Objectives: In this retrospective chart review, we aimed to: (1) replicate previous bilateral sequential TBS effectiveness in a larger cohort of patients at a single centre, (2) present treatment outcome data between unilateral and bilateral TBS approaches, (3) investigate baseline factors associated with our observed outcomes, and (4) examine the sustainability of response, with follow-up data up to 6 months from patients. Methods: We included 161 patients who received TBS (unilateral: n = 64 (40%), 45.55 ± 14.25 years old, 55% females; bilateral: n = 97 (60%), 47.67 ± 15.11 years old, 58% females). Results: Firstly, we observed 47% response and 34% remission in the bilateral group, replicating findings from a smaller naturalistic study from our group; patients receiving unilateral TBS displayed 36% response and 26% remission, with no significant differences found between unilateral and bilateral TBS in remission and response rates. Secondly, bilaterally stimulated patients needed fewer treatments than those stimulated unilaterally (27 vs 29 on average respectively, t [159] = 3.31, p = .001), and had significantly lower anxiety symptoms post treatment (GAD-7) relative to patients receiving unilateral stimulation, F (1,148) = 3.95, p =0.049. Thirdly, no baseline factors were found to predict treatment outcomes. Lastly, after six months, 69% of patients who met the response criteria did not require additional treatment or a change in medication. Conclusions: Our findings support the efficacy and tolerability of TBS in TRD and indicate that bilateral TBS may have a superior anxiolytic effect and offer a slightly faster time to response.

The authors have declared no competing interest.

This study was funded by the St. Joseph's Health Care Foundation.

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This retrospective study has been approved by the Western University office of Human Research Ethics Board at St. Joseph's Health Care London in compliance with the Declaration of Helsinki.

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To protect participant privacy, the data analyzed during the current study are available from the corresponding author on request.