In a double-blind randomized placebo-controlled trial with 34 Japanese patients suffering from treatment-resistant depression, intravenous ketamine (0.5 mg/kg) given twice a week for two weeks did not show a statistically significant advantage over placebo in reducing depression scores when all participants were analyzed together. However, among those who completed the full treatment protocol, ketamine led to a significantly greater reduction in depressive symptoms than placebo. Higher baseline depression severity and body mass index were linked to greater symptom improvement with ketamine. Adverse events were more common with ketamine but no serious events occurred. These results suggest ketamine may be effective for treatment-resistant depression across diverse ethnic groups.
In a double-blind, randomized, placebo-controlled trial, 34 Japanese patients with treatment-resistant depression received four intravenous doses of either ketamine (0.5 mg/kg) or saline. No significant differences emerged between the groups on objective or subjective cognitive function measures. Among ketamine-treated patients, those who responded to treatment (at least 50% reduction on the Montgomery-Åsberg Depression Rating Scale) showed greater improvement in subjective cognitive function than non-responders. Participants with weaker inhibitory control at baseline experienced larger reductions in depressive symptoms after ketamine. Repeated ketamine administration did not worsen cognitive function compared to placebo, suggesting cognitive safety, and baseline cognitive control deficits may predict better treatment response.