Intravenous ketamine at 0.5 mg/kg and 1.0 mg/kg produces rapid antidepressant effects in adults with treatment-resistant depression, with most improvement seen one day after a single 40-minute infusion. Lower doses (0.1 mg/kg and 0.2 mg/kg) did not show consistent benefit. The study compared four ketamine doses against an active placebo (midazolam) in 99 outpatients across six U.S. sites. Higher doses caused more dissociative symptoms and temporary blood pressure increases, but infusions were generally well tolerated. The findings indicate a range of effective subanesthetic doses, with no clear advantage for doses below 0.5 mg/kg.
Repeated doses of ketamine did not reduce depression or suicidal ideation more than placebo in outpatients with severe, treatment-resistant depression and chronic suicidal thoughts. Twenty-six medicated adults received six infusions of ketamine or saline over three weeks. Neither depression severity nor suicidal ideation differed between groups during the infusion phase. At three months, two patients in each group had remitted from depression. The authors suggest that the standard 0.5 mg/kg dose may be insufficient for this severely ill outpatient population.