Eligible studies assessed the antidepressant effects of ketamine on patients with major depressive episodes. To be included patients had to meet clinical criteria for a mood disorder, and be clinically assessed for antidepressant effects for at least 230 minutes post-ketamine.
Most studies administered a dose of 0.5mg/kg via an intravenous infusion over 40 to 60 minutes and used a racemic formulation. The few studies with a placebo control group used saline. Patients in most studies were diagnosed with major depressive disorder; some studies included patients with bipolar disorder. Where reported, co-morbidities were generally anxiety disorders, though single case studies also included patients with substance dependence and prostate cancer. The number of patients with treatment resistant depression varied between studies; no studies administered ketamine to treatment-naive patients. Outcomes were measured using a variety of scales.
The authors did not state how many reviewers selected studies for inclusion.