This study investigates the association between seizure duration during electroconvulsive therapy (ECT) and treatment outcomes in patients with major depressive disorder (MDD). The research is based on data from the Swedish National Quality Register for ECT, analyzing 6998 patients treated between 2012 and 2019. The primary outcome was remission, defined as a Montgomery-Åsberg Depression Rating Scale score below 10 points within one week after ECT. The study found that patients with EEG seizure durations of 60 to 69 seconds had the highest remission rates compared to those with durations less than 20 seconds (OR, 2.17; 95% CI, 1.63-2.88; P < .001). Anticonvulsant medications, such as lamotrigine, were associated with shorter seizure durations and lower remission rates (OR, 0.67; 95% CI, 0.53-0.84; P < .001). The study concludes that longer seizure durations are associated with better treatment outcomes, while anticonvulsant medication during ECT is linked to shorter seizure durations and lower remission rates.This study investigates the association between seizure duration during electroconvulsive therapy (ECT) and treatment outcomes in patients with major depressive disorder (MDD). The research is based on data from the Swedish National Quality Register for ECT, analyzing 6998 patients treated between 2012 and 2019. The primary outcome was remission, defined as a Montgomery-Åsberg Depression Rating Scale score below 10 points within one week after ECT. The study found that patients with EEG seizure durations of 60 to 69 seconds had the highest remission rates compared to those with durations less than 20 seconds (OR, 2.17; 95% CI, 1.63-2.88; P < .001). Anticonvulsant medications, such as lamotrigine, were associated with shorter seizure durations and lower remission rates (OR, 0.67; 95% CI, 0.53-0.84; P < .001). The study concludes that longer seizure durations are associated with better treatment outcomes, while anticonvulsant medication during ECT is linked to shorter seizure durations and lower remission rates.