In a double-blind trial, 99 people with treatment-resistant depression received either a single intravenous dose of ketamine (0.1, 0.2, 0.5, or 1.0 mg/kg) or midazolam (0.045 mg/kg). Among them, 45 had high baseline anxiety and 54 did not. No significant difference in depression improvement was found between the ketamine and midazolam groups for either anxious or nonanxious participants at 1 or 3 days after infusion. The results suggest that ketamine may work similarly for both anxious and nonanxious treatment-resistant depression, unlike some traditional antidepressants.
Among people with treatment-resistant depression, those taking oral benzodiazepines alongside a single intravenous infusion of ketamine showed less improvement in depression scores 24 hours later if they were on higher benzodiazepine doses. The same pattern was not seen in those who received a midazolam placebo. By day 3 after the infusion, benzodiazepine use no longer affected depression scores. The findings suggest that higher doses of benzodiazepines may temporarily weaken ketamine's rapid antidepressant effect.