“Will this actually work for me?” It is the most critical question patients ask before investing time, money, and hope into ketamine therapy. In this episode, we analyze a massive body of research—including a systematic review of 112 studies and a real-world analysis of 77 patients —to find actionable predictors of success.

The results are reassuringly broad: factors like age, sex, depression severity, trauma history, and even the intensity of dissociation do not predict whether ketamine will work. However, the data reveals two powerful signals that every patient should know:

The “Line in the Sand”: The strongest negative predictor is pharmacological resistance. Patients who have failed more than six previous antidepressant trials were significantly less likely to respond to ketamine.

The “Perfect” Positive Signal: Researchers identified an early marker of success after just the second infusion. A tiny symptom reduction of just 4.1% on the PHQ-9 scale carried a Positive Predictive Value of 1.0—meaning 100% of patients who hit this mark went on to achieve a clinical response.

Crucially, we explain why early non-improvement does not mean failure, as nearly half of patients who showed zero improvement after dose two still achieved a response by the end of treatment. Join us to learn why ketamine might need to be considered earlier in the treatment timeline, before pharmacological resistance sets in.

Reference:

Syed, O. A. (2025). Predictors of the antidepressant effects of ketamine and psychedelic substances [Master’s thesis, University of Toronto]. TSpace Repository.

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