A Flawed Ketamine Trial?

The KARMA-Dep2 trial delivered a shocking headline: up to eight serial ketamine infusions were no better than the midazolam placebo for hospitalized adults with moderate to severe depression. In an era of intense hope for ketamine's rapid antidepressant effects, this result demands a closer look. This episode critically dissects why this large, pragmatic trial may have failed to show a significant difference, focusing on a central challenge in ketamine research: blinding. The Active Placebo Problem: The trial used midazolam as an active placebo to mimic the transient side effects (like sedation and disorientation) of ketamine. However, previous meta-analyses (Wilkinson et al., 2019) show that midazolam itself produces a substantial placebo/expectancy effect (around an 18% response rate), effectively setting a high floor that makes the pharmacological benefit of ketamine harder to detect. The Unblinding Issue: We contrast the KARMA-Dep2 outcome with the Dwyer et al. (2021) adolescent trial, where ketamine was significantly better than midazolam. Crucially, the adolescent study revealed a massive confound: 10 out of 10 patients on ketamine correctly guessed their treatment, illustrating the "functional unblinding" that allows expectation to heavily influence results. The Measurement Challenge: We discuss the inherent difficulty of using scales designed for slow-acting drugs (like MADRS and HAMD) to measure ketamine's rapid antidepressant effects, leading to measurement workarounds like carrying over scores for symptoms like sleep and appetite. The core question remains: Does midazolam give a truly realistic estimate of ketamine's effect, or does chasing the "perfect blind" with an active placebo simply obscure the real-world value of a drug whose unique, powerful experience is inseparable from its clinical benefit? Resources: Wilkinson, S. T., Farmer, C., Ballard, E. D., Mathew, S. J., Grunebaum, M. F., Murrough, J. W., Sos, P., Wang, G., Gueorguieva, R., & Zarate, C. A., Jr. (2019). Impact of midazolam vs. saline on effect size estimates in controlled trials of ketamine as a rapid-acting antidepressant. Neuropsychopharmacology, 44, 1233–1238. https://doi.org/10.1038/s41386-019-0317-8 Dwyer, J. B., Landeros-Weisenberger, A., Johnson, J. A., Londono Tobon, A., Flores, J. M., Nasir, M., Couloures, K., Sanacora, G., & Bloch, M. H. (2021). Efficacy of Intravenous Ketamine in Adolescent Treatment-Resistant Depression: A Randomized Midazolam-Controlled Trial. American Journal of Psychiatry, 178(4), 352–362. https://doi.org/10.1176/appi.ajp.2020.20010018 Jelovac, A., McCaffrey, C., Terao, M., Shanahan, E., Whooley, E., McDonagh, K., McDonogh, S., Loughran, O., Shackleton, E., Igoe, A., Thompson, S., Mohamed, E., Nguyen, D., O'Neill, C., Walsh, C., & McLoughlin, D. M. (2025). Serial Ketamine Infusions as Adjunctive Therapy to Inpatient Care for Depression: The KARMA-Dep 2 Randomized Clinical Trial. JAMA Psychiatry. https://doi.org/10.1001/jamapsychiatry.2025.3019