Anhedonia, a core symptom of depression linked to suicidality and reduced quality of life, often resists standard treatments. In 42 patients with treatment-resistant depression, eight ketamine infusions added to ongoing therapy significantly reduced anhedonia, as measured by the Snaith-Hamilton Pleasure Scale. This reduction in anhedonia appeared to mediate ketamine's overall antidepressant effect. However, the benefit was observed only among patients not using benzodiazepines. The findings require confirmation in a larger randomized placebo-controlled trial.
In an open-label observational study, 13 patients with treatment-resistant bipolar depression received eight intravenous infusions of 0.5 mg/kg ketamine over four weeks. After the seventh infusion, 61.5% responded and 46.2% achieved remission. Responders also showed a significant antisuicidal effect. Ketamine caused a transient rise in blood pressure and increased dissociative symptoms, but no manic switch or serious adverse events occurred. The findings suggest ketamine is a safe and feasible add-on treatment for this population.