Clinical response to a second course of electroconvulsive therapy: Within- and between-person analysis of a...

Electroconvulsive therapy (ECT) is an established treatment for a host of severe mental disorders, and many patients undergo multiple courses across their illness trajectory. In this study, we investigated whether clinical response to ECT remains consistent across successive courses and whether prior response predicts future outcomes. We analyzed a retrospective cohort of 351 ECT courses conducted in adult inpatients from 2009 to 2015 in Brazil. The main outcome was change in Clinical Global Impression scores. For patients with more than one course (n = 25), we compared responses between the first and second series using paired t-tests and correlation analysis. We also applied mixed-effects regression models to the full sample to disentangle within-person and between-person variability. In the second course, patients had significantly less clinical improvement compared to the first (p = 0.003), despite a strong correlation in response within individuals (r = 0.77). Mixed models confirmed a significant within-person decline in ECT effectiveness (β = 0.53, p = 0.004), while between-person differences were not significant. These findings are limited by the small sample of people with two courses, but suggest that while repeated ECT courses may yield diminishing average benefit, patients tend to retain stable individual response patterns, and prior response may thus inform clinical expectations and decisions.