After six intravenous injections of 0.5 mg/kg ketamine, both patients with melancholic depression (30 individuals) and those with non-melancholic depression (105 individuals) showed similar improvement in anhedonic symptoms. The antianhedonic response rate was 43.3% in the melancholic group versus 50.5% in the non-melancholic group, a difference that was not statistically significant. Remission rates were also similar: 20.0% and 21.0%, respectively. By day 26, the melancholic group had significantly lower anhedonia scores on the Montgomery–Åsberg Depression Rating Scale compared to the non-melancholic group. Ketamine appears equally effective for reducing anhedonia in both melancholic and non-melancholic depression.
Patients with depression and a higher baseline body mass index (BMI) experienced greater reductions in depressive symptoms after six intravenous ketamine infusions compared with those with a lower baseline BMI. In a study of 135 patients (103 with major depressive disorder, 32 with bipolar depression), those with a lower BMI (under 26) showed a significantly higher response rate after the first infusion (40.3% vs. 23.6%), but this difference disappeared by the sixth infusion. The overall change in depression scores over time differed significantly between the groups, with the higher-BMI group showing greater improvement. The findings are from an exploratory, post-hoc analysis of an open-label, single-arm trial.