Two intravenous infusions of ketamine (0.5 mg/kg) given 24 hours apart, added to usual treatment, led to full remission of suicidal ideas by day 3 in 63.0% of hospitalized patients with suicidal ideation, compared to 31.6% with placebo. The benefit was strongest in patients with bipolar disorder (odds ratio 14.1), not significant in those with depressive disorder (odds ratio 1.3), and intermediate for other disorders (odds ratio 3.7). At six weeks, remission remained high in the ketamine group (69.5% vs 56.3%) but was no longer statistically significant. Side effects were limited, with no manic or psychotic symptoms observed. An analgesic effect on mental pain may explain the anti-suicidal action.
People with first episode psychosis and treatment-resistant schizophrenia show reduced ability to stabilize their decision-making strategies in uncertain environments, resembling effects previously seen with the drug ketamine. In two studies, participants completed a probabilistic reversal learning task. Those with first episode psychosis made more errors and shifted strategies too often after misleading feedback. The treatment-resistant schizophrenia group also shifted strategies more, though their overall accuracy was not significantly reduced. Computational modeling revealed that only the treatment-resistant schizophrenia group showed altered confidence-based modulation of responding, similar to ketamine effects, though these modeling results are considered preliminary due to model limitations.